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	$228.30	11.814%	$255.2714	$255.27	$255.25	$255.30
Purchase #2	$98.38	10.411%	$108.6223	$108.62	$108.60	$108.60
Purchase #3	$247.32	12.267%	$277.6587	$277.66	$277.65	$277.70
Purchase #4	$59.91	8.260%	$64.8586	$64.86	$64.85	$64.90
Purchase #5	$54.37	5.142%	$57.1657	$57.17	$57.15	$57.20
Purchase #6	$122.85	12.148%	$137.7738	$137.77	$137.75	$137.80
Purchase #7	$94.70	12.560%	$106.5943	$106.59	$106.60	$106.60
7 purchase totals =	$905.83		$1,007.9448	$1,007.94	$1,007.85	$1,008.10