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	$201.58	10.287%	$222.3165	$222.32	$222.30	$222.30
Purchase #2	$228.46	3.545%	$236.5589	$236.56	$236.55	$236.60
Purchase #3	$223.60	11.782%	$249.9446	$249.94	$249.95	$249.90
Purchase #4	$83.33	10.339%	$91.9455	$91.95	$91.95	$91.90
Purchase #5	$89.34	12.316%	$100.3431	$100.34	$100.35	$100.30
Purchase #6	$216.73	3.733%	$224.8205	$224.82	$224.80	$224.80
Purchase #7	$105.42	7.327%	$113.1441	$113.14	$113.15	$113.10
7 purchase totals =	$1,148.46		$1,239.0732	$1,239.07	$1,239.05	$1,238.90