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	$208.83	5.511%	$220.3386	$220.34	$220.35	$220.30
Purchase #2	$34.79	13.597%	$39.5204	$39.52	$39.50	$39.50
Purchase #3	$33.28	13.565%	$37.7944	$37.79	$37.80	$37.80
Purchase #4	$39.33	7.547%	$42.2982	$42.30	$42.30	$42.30
Purchase #5	$75.73	8.350%	$82.0535	$82.05	$82.05	$82.10
Purchase #6	$86.51	3.384%	$89.4375	$89.44	$89.45	$89.40
Purchase #7	$46.93	3.782%	$48.7049	$48.70	$48.70	$48.70
7 purchase totals =	$525.40		$560.1475	$560.14	$560.15	$560.10