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	$87.57	5.317%	$92.2261	$92.23	$92.25	$92.20
Purchase #2	$220.75	13.156%	$249.7919	$249.79	$249.80	$249.80
Purchase #3	$145.53	9.719%	$159.6741	$159.67	$159.65	$159.70
Purchase #4	$28.51	11.325%	$31.7388	$31.74	$31.75	$31.70
Purchase #5	$56.58	6.791%	$60.4223	$60.42	$60.40	$60.40
Purchase #6	$109.69	12.283%	$123.1632	$123.16	$123.15	$123.20
Purchase #7	$86.63	4.427%	$90.4651	$90.47	$90.45	$90.50
7 purchase totals =	$735.26		$807.4815	$807.48	$807.45	$807.50