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	$64.83	9.167%	$70.773	$70.77	$70.75	$70.80
Purchase #2	$149.72	6.580%	$159.5716	$159.57	$159.55	$159.60
Purchase #3	$22.91	7.427%	$24.6115	$24.61	$24.60	$24.60
Purchase #4	$152.73	5.521%	$161.1622	$161.16	$161.15	$161.20
Purchase #5	$166.50	13.190%	$188.4614	$188.46	$188.45	$188.50
Purchase #6	$187.39	13.700%	$213.0624	$213.06	$213.05	$213.10
Purchase #7	$170.93	8.244%	$185.0215	$185.02	$185.00	$185.00
7 purchase totals =	$915.01		$1,002.6636	$1,002.65	$1,002.55	$1,002.80