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	$99.61	13.305%	$112.8631	$112.86	$112.85	$112.90
Purchase #2	$189.40	10.620%	$209.5143	$209.51	$209.50	$209.50
Purchase #3	$216.70	11.850%	$242.379	$242.38	$242.40	$242.40
Purchase #4	$117.86	6.833%	$125.9134	$125.91	$125.90	$125.90
Purchase #5	$138.25	4.871%	$144.9842	$144.98	$145.00	$145.00
Purchase #6	$204.27	9.553%	$223.7839	$223.78	$223.80	$223.80
Purchase #7	$222.54	11.848%	$248.9065	$248.91	$248.90	$248.90
7 purchase totals =	$1,188.63		$1,308.3444	$1,308.33	$1,308.35	$1,308.40