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	$223.64	12.512%	$251.6218	$251.62	$251.60	$251.60
Purchase #2	$30.69	10.191%	$33.8176	$33.82	$33.80	$33.80
Purchase #3	$57.77	5.720%	$61.0744	$61.07	$61.05	$61.10
Purchase #4	$108.63	10.432%	$119.9623	$119.96	$119.95	$120.00
Purchase #5	$81.25	9.725%	$89.1516	$89.15	$89.15	$89.20
Purchase #6	$224.52	13.799%	$255.5015	$255.50	$255.50	$255.50
Purchase #7	$234.64	13.821%	$267.0696	$267.07	$267.05	$267.10
7 purchase totals =	$961.14		$1,078.1988	$1,078.19	$1,078.10	$1,078.30