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	$82.93	8.651%	$90.1043	$90.10	$90.10	$90.10
Purchase #2	$121.95	4.525%	$127.4682	$127.47	$127.45	$127.50
Purchase #3	$69.31	8.620%	$75.2845	$75.28	$75.30	$75.30
Purchase #4	$151.79	9.275%	$165.8685	$165.87	$165.85	$165.90
Purchase #5	$199.33	5.315%	$209.9244	$209.92	$209.90	$209.90
Purchase #6	$135.63	12.208%	$152.1877	$152.19	$152.20	$152.20
Purchase #7	$118.72	5.333%	$125.0513	$125.05	$125.05	$125.10
7 purchase totals =	$879.66		$945.8889	$945.88	$945.85	$946.00