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	$49.52	10.344%	$54.6423	$54.64	$54.65	$54.60
Purchase #2	$63.64	7.388%	$68.3417	$68.34	$68.35	$68.30
Purchase #3	$164.83	3.387%	$170.4128	$170.41	$170.40	$170.40
Purchase #4	$71.45	8.561%	$77.5668	$77.57	$77.55	$77.60
Purchase #5	$54.81	12.154%	$61.4716	$61.47	$61.45	$61.50
Purchase #6	$125.26	9.286%	$136.8916	$136.89	$136.90	$136.90
Purchase #7	$80.46	5.829%	$85.15	$85.15	$85.15	$85.20
7 purchase totals =	$609.97		$654.4768	$654.47	$654.45	$654.50