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	$37.60	5.372%	$39.6199	$39.62	$39.60	$39.60
Purchase #2	$239.52	11.575%	$267.2444	$267.24	$267.25	$267.20
Purchase #3	$226.35	12.279%	$254.1435	$254.14	$254.15	$254.10
Purchase #4	$237.59	4.249%	$247.6852	$247.69	$247.70	$247.70
Purchase #5	$58.85	9.645%	$64.5261	$64.53	$64.55	$64.50
Purchase #6	$32.52	4.198%	$33.8852	$33.89	$33.90	$33.90
Purchase #7	$208.96	12.687%	$235.4708	$235.47	$235.45	$235.50
7 purchase totals =	$1,041.39		$1,142.5751	$1,142.58	$1,142.60	$1,142.50