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	$46.59	9.765%	$51.1395	$51.14	$51.15	$51.10
Purchase #2	$37.82	7.169%	$40.5313	$40.53	$40.55	$40.50
Purchase #3	$68.85	5.428%	$72.5872	$72.59	$72.60	$72.60
Purchase #4	$202.62	10.238%	$223.3642	$223.36	$223.35	$223.40
Purchase #5	$247.48	10.451%	$273.3441	$273.34	$273.35	$273.30
Purchase #6	$36.33	8.114%	$39.2778	$39.28	$39.30	$39.30
Purchase #7	$196.81	9.766%	$216.0305	$216.03	$216.05	$216.00
7 purchase totals =	$836.50		$916.2746	$916.27	$916.35	$916.20