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	$223.28	12.805%	$251.871	$251.87	$251.85	$251.90
Purchase #2	$144.30	4.568%	$150.8916	$150.89	$150.90	$150.90
Purchase #3	$34.48	10.513%	$38.1049	$38.10	$38.10	$38.10
Purchase #4	$69.90	10.414%	$77.1794	$77.18	$77.20	$77.20
Purchase #5	$223.92	9.634%	$245.4925	$245.49	$245.50	$245.50
Purchase #6	$71.69	9.261%	$78.3292	$78.33	$78.35	$78.30
Purchase #7	$65.89	7.621%	$70.9115	$70.91	$70.90	$70.90
7 purchase totals =	$833.46		$912.7801	$912.77	$912.80	$912.80