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	$166.55	13.729%	$189.4156	$189.42	$189.40	$189.40
Purchase #2	$216.76	5.821%	$229.3776	$229.38	$229.40	$229.40
Purchase #3	$203.42	11.841%	$227.507	$227.51	$227.50	$227.50
Purchase #4	$158.72	5.702%	$167.7702	$167.77	$167.75	$167.80
Purchase #5	$163.55	5.691%	$172.8576	$172.86	$172.85	$172.90
Purchase #6	$236.42	5.792%	$250.1134	$250.11	$250.10	$250.10
Purchase #7	$81.94	4.486%	$85.6158	$85.62	$85.60	$85.60
7 purchase totals =	$1,227.36		$1,322.6572	$1,322.67	$1,322.60	$1,322.70