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	$30.90	9.114%	$33.7162	$33.72	$33.70	$33.70
Purchase #2	$140.94	7.680%	$151.7642	$151.76	$151.75	$151.80
Purchase #3	$185.49	7.523%	$199.4444	$199.44	$199.45	$199.40
Purchase #4	$89.96	3.538%	$93.1428	$93.14	$93.15	$93.10
Purchase #5	$101.42	11.465%	$113.0478	$113.05	$113.05	$113.00
Purchase #6	$136.28	11.339%	$151.7328	$151.73	$151.75	$151.70
Purchase #7	$72.74	8.495%	$78.9193	$78.92	$78.90	$78.90
7 purchase totals =	$757.73		$821.7675	$821.76	$821.75	$821.60