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	$238.81	10.249%	$263.2856	$263.29	$263.30	$263.30
Purchase #2	$246.30	12.539%	$277.1836	$277.18	$277.20	$277.20
Purchase #3	$78.31	13.817%	$89.1301	$89.13	$89.15	$89.10
Purchase #4	$58.83	10.318%	$64.9001	$64.90	$64.90	$64.90
Purchase #5	$230.64	13.863%	$262.6136	$262.61	$262.60	$262.60
Purchase #6	$246.35	4.531%	$257.5121	$257.51	$257.50	$257.50
Purchase #7	$89.87	10.206%	$99.0421	$99.04	$99.05	$99.00
7 purchase totals =	$1,189.11		$1,313.6672	$1,313.66	$1,313.70	$1,313.60