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	$37.86	13.328%	$42.906	$42.91	$42.90	$42.90
Purchase #2	$171.31	12.117%	$192.0676	$192.07	$192.05	$192.10
Purchase #3	$23.78	5.542%	$25.0979	$25.10	$25.10	$25.10
Purchase #4	$79.53	7.105%	$85.1806	$85.18	$85.20	$85.20
Purchase #5	$22.27	13.869%	$25.3586	$25.36	$25.35	$25.40
Purchase #6	$209.56	10.531%	$231.6288	$231.63	$231.65	$231.60
Purchase #7	$93.36	10.342%	$103.0153	$103.02	$103.00	$103.00
7 purchase totals =	$637.67		$705.2548	$705.27	$705.25	$705.30