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	$243.34	13.871%	$277.0937	$277.09	$277.10	$277.10
Purchase #2	$7.44	4.179%	$7.7509	$7.75	$7.75	$7.80
Purchase #3	$188.50	11.846%	$210.8297	$210.83	$210.85	$210.80
Purchase #4	$33.30	4.635%	$34.8435	$34.84	$34.85	$34.80
Purchase #5	$185.78	5.806%	$196.5664	$196.57	$196.55	$196.60
Purchase #6	$129.39	7.528%	$139.1305	$139.13	$139.15	$139.10
Purchase #7	$132.77	4.590%	$138.8641	$138.86	$138.85	$138.90
7 purchase totals =	$920.52		$1,005.0788	$1,005.07	$1,005.10	$1,005.10