Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$93.31	7.623%	$100.423	$100.42	$100.40	$100.40
Purchase #2	$70.37	10.757%	$77.9397	$77.94	$77.95	$77.90
Purchase #3	$92.90	13.225%	$105.186	$105.19	$105.20	$105.20
Purchase #4	$212.90	11.827%	$238.0797	$238.08	$238.10	$238.10
Purchase #5	$71.39	9.276%	$78.0121	$78.01	$78.00	$78.00
Purchase #6	$231.25	12.571%	$260.3204	$260.32	$260.30	$260.30
Purchase #7	$235.28	11.154%	$261.5231	$261.52	$261.50	$261.50
7 purchase totals =	$1,007.40		$1,121.4840	$1,121.48	$1,121.45	$1,121.40