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	$117.91	13.399%	$133.7088	$133.71	$133.70	$133.70
Purchase #2	$31.31	4.134%	$32.6044	$32.60	$32.60	$32.60
Purchase #3	$37.51	11.358%	$41.7704	$41.77	$41.75	$41.80
Purchase #4	$37.86	6.131%	$40.1812	$40.18	$40.20	$40.20
Purchase #5	$51.81	10.327%	$57.1604	$57.16	$57.15	$57.20
Purchase #6	$120.77	3.134%	$124.5549	$124.55	$124.55	$124.60
Purchase #7	$173.94	10.129%	$191.5584	$191.56	$191.55	$191.60
7 purchase totals =	$571.11		$621.5385	$621.53	$621.50	$621.70