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	$33.90	9.485%	$37.1154	$37.12	$37.10	$37.10
Purchase #2	$163.49	8.210%	$176.9125	$176.91	$176.90	$176.90
Purchase #3	$53.61	13.821%	$61.0194	$61.02	$61.00	$61.00
Purchase #4	$62.52	8.585%	$67.8873	$67.89	$67.90	$67.90
Purchase #5	$202.58	5.199%	$213.1121	$213.11	$213.10	$213.10
Purchase #6	$214.82	8.616%	$233.3289	$233.33	$233.35	$233.30
Purchase #7	$161.41	6.668%	$172.1728	$172.17	$172.15	$172.20
7 purchase totals =	$892.33		$961.5484	$961.55	$961.50	$961.50