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	$115.83	6.659%	$123.5431	$123.54	$123.55	$123.50
Purchase #2	$48.38	10.399%	$53.411	$53.41	$53.40	$53.40
Purchase #3	$130.83	8.393%	$141.8106	$141.81	$141.80	$141.80
Purchase #4	$61.29	3.263%	$63.2899	$63.29	$63.30	$63.30
Purchase #5	$91.41	4.859%	$95.8516	$95.85	$95.85	$95.90
Purchase #6	$132.38	5.130%	$139.1711	$139.17	$139.15	$139.20
Purchase #7	$55.38	5.312%	$58.3218	$58.32	$58.30	$58.30
7 purchase totals =	$635.50		$675.3991	$675.39	$675.35	$675.40