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	$99.26	12.229%	$111.3985	$111.40	$111.40	$111.40
Purchase #2	$236.27	11.331%	$263.0418	$263.04	$263.05	$263.00
Purchase #3	$41.61	3.344%	$43.0014	$43.00	$43.00	$43.00
Purchase #4	$236.66	7.779%	$255.0698	$255.07	$255.05	$255.10
Purchase #5	$194.88	12.151%	$218.5599	$218.56	$218.55	$218.60
Purchase #6	$80.49	4.285%	$83.939	$83.94	$83.95	$83.90
Purchase #7	$9.84	6.163%	$10.4464	$10.45	$10.45	$10.40
7 purchase totals =	$899.01		$985.4568	$985.46	$985.45	$985.40