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	$55.58	12.572%	$62.5675	$62.57	$62.55	$62.60
Purchase #2	$57.29	3.216%	$59.1324	$59.13	$59.15	$59.10
Purchase #3	$56.39	9.434%	$61.7098	$61.71	$61.70	$61.70
Purchase #4	$241.33	13.271%	$273.3569	$273.36	$273.35	$273.40
Purchase #5	$65.54	9.317%	$71.6464	$71.65	$71.65	$71.60
Purchase #6	$39.94	4.676%	$41.8076	$41.81	$41.80	$41.80
Purchase #7	$230.29	10.112%	$253.5769	$253.58	$253.60	$253.60
7 purchase totals =	$746.36		$823.7975	$823.81	$823.80	$823.80