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	$88.30	13.561%	$100.2744	$100.27	$100.25	$100.30
Purchase #2	$205.51	6.274%	$218.4037	$218.40	$218.40	$218.40
Purchase #3	$139.78	8.848%	$152.1477	$152.15	$152.15	$152.10
Purchase #4	$23.50	10.202%	$25.8975	$25.90	$25.90	$25.90
Purchase #5	$32.69	10.660%	$36.1748	$36.17	$36.15	$36.20
Purchase #6	$225.59	13.482%	$256.004	$256.00	$256.00	$256.00
Purchase #7	$155.96	4.220%	$162.5415	$162.54	$162.55	$162.50
7 purchase totals =	$871.33		$951.4436	$951.43	$951.40	$951.40