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	$37.89	6.420%	$40.3225	$40.32	$40.30	$40.30
Purchase #2	$111.95	11.459%	$124.7784	$124.78	$124.80	$124.80
Purchase #3	$196.41	12.832%	$221.6133	$221.61	$221.60	$221.60
Purchase #4	$24.55	9.574%	$26.9004	$26.90	$26.90	$26.90
Purchase #5	$180.81	12.563%	$203.5252	$203.53	$203.55	$203.50
Purchase #6	$149.53	6.864%	$159.7937	$159.79	$159.80	$159.80
Purchase #7	$72.52	8.775%	$78.8836	$78.88	$78.90	$78.90
7 purchase totals =	$773.66		$855.8171	$855.81	$855.85	$855.80