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	$12.28	7.437%	$13.1933	$13.19	$13.20	$13.20
Purchase #2	$99.52	12.185%	$111.6465	$111.65	$111.65	$111.60
Purchase #3	$244.28	9.549%	$267.6063	$267.61	$267.60	$267.60
Purchase #4	$238.34	9.832%	$261.7736	$261.77	$261.75	$261.80
Purchase #5	$153.55	7.651%	$165.2981	$165.30	$165.30	$165.30
Purchase #6	$211.70	10.829%	$234.625	$234.63	$234.65	$234.60
Purchase #7	$24.89	9.774%	$27.3227	$27.32	$27.30	$27.30
7 purchase totals =	$984.56		$1,081.4655	$1,081.47	$1,081.45	$1,081.40