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	$33.94	9.837%	$37.2787	$37.28	$37.30	$37.30
Purchase #2	$90.73	12.744%	$102.2926	$102.29	$102.30	$102.30
Purchase #3	$102.63	8.788%	$111.6491	$111.65	$111.65	$111.60
Purchase #4	$219.74	4.741%	$230.1579	$230.16	$230.15	$230.20
Purchase #5	$145.67	3.391%	$150.6097	$150.61	$150.60	$150.60
Purchase #6	$93.26	9.704%	$102.31	$102.31	$102.30	$102.30
Purchase #7	$151.85	6.636%	$161.9268	$161.93	$161.95	$161.90
7 purchase totals =	$837.82		$896.2248	$896.23	$896.25	$896.20