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	$238.90	13.276%	$270.6164	$270.62	$270.60	$270.60
Purchase #2	$230.83	10.761%	$255.6696	$255.67	$255.65	$255.70
Purchase #3	$205.32	8.738%	$223.2609	$223.26	$223.25	$223.30
Purchase #4	$83.43	9.131%	$91.048	$91.05	$91.05	$91.00
Purchase #5	$245.59	3.620%	$254.4804	$254.48	$254.50	$254.50
Purchase #6	$136.52	8.314%	$147.8703	$147.87	$147.85	$147.90
Purchase #7	$237.65	5.228%	$250.0743	$250.07	$250.05	$250.10
7 purchase totals =	$1,378.24		$1,493.0199	$1,493.02	$1,492.95	$1,493.10