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	$232.91	12.724%	$262.5455	$262.55	$262.55	$262.50
Purchase #2	$82.40	10.160%	$90.7718	$90.77	$90.75	$90.80
Purchase #3	$44.73	9.679%	$49.0594	$49.06	$49.05	$49.10
Purchase #4	$121.39	10.762%	$134.454	$134.45	$134.45	$134.50
Purchase #5	$124.57	4.658%	$130.3725	$130.37	$130.35	$130.40
Purchase #6	$169.46	13.818%	$192.876	$192.88	$192.90	$192.90
Purchase #7	$222.34	9.270%	$242.9509	$242.95	$242.95	$243.00
7 purchase totals =	$997.80		$1,103.0301	$1,103.03	$1,103.00	$1,103.20