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	$132.71	11.172%	$147.5364	$147.54	$147.55	$147.50
Purchase #2	$136.90	6.754%	$146.1462	$146.15	$146.15	$146.10
Purchase #3	$205.63	3.853%	$213.5529	$213.55	$213.55	$213.60
Purchase #4	$63.76	5.703%	$67.3962	$67.40	$67.40	$67.40
Purchase #5	$72.52	9.792%	$79.6212	$79.62	$79.60	$79.60
Purchase #6	$125.64	13.521%	$142.6278	$142.63	$142.65	$142.60
Purchase #7	$56.65	8.243%	$61.3197	$61.32	$61.30	$61.30
7 purchase totals =	$793.81		$858.2004	$858.21	$858.20	$858.10