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	$15.31	13.797%	$17.4223	$17.42	$17.40	$17.40
Purchase #2	$131.54	11.417%	$146.5579	$146.56	$146.55	$146.60
Purchase #3	$155.29	4.103%	$161.6615	$161.66	$161.65	$161.70
Purchase #4	$33.41	12.313%	$37.5238	$37.52	$37.50	$37.50
Purchase #5	$174.48	6.563%	$185.9311	$185.93	$185.95	$185.90
Purchase #6	$54.91	7.672%	$59.1227	$59.12	$59.10	$59.10
Purchase #7	$152.96	6.348%	$162.6699	$162.67	$162.65	$162.70
7 purchase totals =	$717.90		$770.8892	$770.88	$770.80	$770.90