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	$100.33	3.147%	$103.4874	$103.49	$103.50	$103.50
Purchase #2	$172.89	8.722%	$187.9695	$187.97	$187.95	$188.00
Purchase #3	$20.33	4.407%	$21.2259	$21.23	$21.25	$21.20
Purchase #4	$234.68	6.624%	$250.2252	$250.23	$250.25	$250.20
Purchase #5	$222.39	4.122%	$231.5569	$231.56	$231.55	$231.60
Purchase #6	$162.94	9.370%	$178.2075	$178.21	$178.20	$178.20
Purchase #7	$91.67	4.214%	$95.533	$95.53	$95.55	$95.50
7 purchase totals =	$1,005.23		$1,068.2054	$1,068.22	$1,068.25	$1,068.20