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	$121.53	13.119%	$137.4735	$137.47	$137.45	$137.50
Purchase #2	$49.82	12.318%	$55.9568	$55.96	$55.95	$56.00
Purchase #3	$10.76	6.108%	$11.4172	$11.42	$11.40	$11.40
Purchase #4	$249.43	3.679%	$258.6065	$258.61	$258.60	$258.60
Purchase #5	$161.50	6.576%	$172.1202	$172.12	$172.10	$172.10
Purchase #6	$170.73	8.426%	$185.1157	$185.12	$185.10	$185.10
Purchase #7	$79.57	11.549%	$88.7595	$88.76	$88.75	$88.80
7 purchase totals =	$843.34		$909.4494	$909.46	$909.35	$909.50