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	$25.49	10.317%	$28.1198	$28.12	$28.10	$28.10
Purchase #2	$174.85	8.797%	$190.2316	$190.23	$190.25	$190.20
Purchase #3	$231.52	5.446%	$244.1286	$244.13	$244.15	$244.10
Purchase #4	$78.65	13.652%	$89.3873	$89.39	$89.40	$89.40
Purchase #5	$209.62	12.505%	$235.833	$235.83	$235.85	$235.80
Purchase #6	$62.67	3.620%	$64.9387	$64.94	$64.95	$64.90
Purchase #7	$85.52	8.680%	$92.9431	$92.94	$92.95	$92.90
7 purchase totals =	$868.32		$945.5821	$945.58	$945.65	$945.40