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	$46.70	3.238%	$48.2121	$48.21	$48.20	$48.20
Purchase #2	$56.61	6.145%	$60.0887	$60.09	$60.10	$60.10
Purchase #3	$11.83	13.174%	$13.3885	$13.39	$13.40	$13.40
Purchase #4	$249.51	8.367%	$270.3865	$270.39	$270.40	$270.40
Purchase #5	$156.39	10.318%	$172.5263	$172.53	$172.55	$172.50
Purchase #6	$169.56	12.364%	$190.5244	$190.52	$190.50	$190.50
Purchase #7	$59.57	6.404%	$63.3849	$63.38	$63.40	$63.40
7 purchase totals =	$750.17		$818.5114	$818.51	$818.55	$818.50