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	$223.51	13.326%	$253.2949	$253.29	$253.30	$253.30
Purchase #2	$234.85	7.460%	$252.3698	$252.37	$252.35	$252.40
Purchase #3	$89.77	5.211%	$94.4479	$94.45	$94.45	$94.40
Purchase #4	$231.55	3.602%	$239.8904	$239.89	$239.90	$239.90
Purchase #5	$78.30	9.689%	$85.8865	$85.89	$85.90	$85.90
Purchase #6	$125.51	5.120%	$131.9361	$131.94	$131.95	$131.90
Purchase #7	$100.75	11.723%	$112.5609	$112.56	$112.55	$112.60
7 purchase totals =	$1,084.24		$1,170.3865	$1,170.39	$1,170.40	$1,170.40