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	$46.42	7.847%	$50.0626	$50.06	$50.05	$50.10
Purchase #2	$178.50	3.170%	$184.1585	$184.16	$184.15	$184.20
Purchase #3	$61.59	13.199%	$69.7193	$69.72	$69.70	$69.70
Purchase #4	$66.90	7.129%	$71.6693	$71.67	$71.65	$71.70
Purchase #5	$211.64	5.586%	$223.4622	$223.46	$223.45	$223.50
Purchase #6	$123.52	12.810%	$139.3429	$139.34	$139.35	$139.30
Purchase #7	$110.39	13.680%	$125.4914	$125.49	$125.50	$125.50
7 purchase totals =	$798.96		$863.9062	$863.90	$863.85	$864.00