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	$159.41	4.624%	$166.7811	$166.78	$166.80	$166.80
Purchase #2	$6.65	3.665%	$6.8937	$6.89	$6.90	$6.90
Purchase #3	$34.51	7.476%	$37.09	$37.09	$37.10	$37.10
Purchase #4	$76.50	5.158%	$80.4459	$80.45	$80.45	$80.40
Purchase #5	$130.25	8.571%	$141.4137	$141.41	$141.40	$141.40
Purchase #6	$34.96	5.714%	$36.9576	$36.96	$36.95	$37.00
Purchase #7	$210.54	13.195%	$238.3208	$238.32	$238.30	$238.30
7 purchase totals =	$652.82		$707.9028	$707.90	$707.90	$707.90