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	$57.50	8.125%	$62.1719	$62.17	$62.15	$62.20
Purchase #2	$90.33	10.375%	$99.7017	$99.70	$99.70	$99.70
Purchase #3	$68.65	11.467%	$76.5221	$76.52	$76.50	$76.50
Purchase #4	$76.55	11.481%	$85.3387	$85.34	$85.35	$85.30
Purchase #5	$105.98	3.427%	$109.6119	$109.61	$109.60	$109.60
Purchase #6	$55.85	10.364%	$61.6383	$61.64	$61.65	$61.60
Purchase #7	$51.87	12.651%	$58.4321	$58.43	$58.45	$58.40
7 purchase totals =	$506.73		$553.4167	$553.41	$553.40	$553.30