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	$152.61	9.726%	$167.4528	$167.45	$167.45	$167.50
Purchase #2	$35.94	11.699%	$40.1446	$40.14	$40.15	$40.10
Purchase #3	$22.45	6.311%	$23.8668	$23.87	$23.85	$23.90
Purchase #4	$166.95	10.570%	$184.5966	$184.60	$184.60	$184.60
Purchase #5	$41.53	8.868%	$45.2129	$45.21	$45.20	$45.20
Purchase #6	$149.34	12.377%	$167.8238	$167.82	$167.80	$167.80
Purchase #7	$36.52	9.589%	$40.0219	$40.02	$40.00	$40.00
7 purchase totals =	$605.34		$669.1194	$669.11	$669.05	$669.10