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	$91.51	9.628%	$100.3206	$100.32	$100.30	$100.30
Purchase #2	$203.38	12.551%	$228.9062	$228.91	$228.90	$228.90
Purchase #3	$139.96	11.112%	$155.5124	$155.51	$155.50	$155.50
Purchase #4	$113.54	9.783%	$124.6476	$124.65	$124.65	$124.60
Purchase #5	$162.85	9.862%	$178.9103	$178.91	$178.90	$178.90
Purchase #6	$13.34	8.540%	$14.4792	$14.48	$14.50	$14.50
Purchase #7	$116.96	7.141%	$125.3121	$125.31	$125.30	$125.30
7 purchase totals =	$841.54		$928.0884	$928.09	$928.05	$928.00