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	$37.63	7.190%	$40.3356	$40.34	$40.35	$40.30
Purchase #2	$205.58	4.722%	$215.2875	$215.29	$215.30	$215.30
Purchase #3	$124.26	11.863%	$139.001	$139.00	$139.00	$139.00
Purchase #4	$74.95	3.358%	$77.4668	$77.47	$77.45	$77.50
Purchase #5	$124.79	11.680%	$139.3655	$139.37	$139.35	$139.40
Purchase #6	$71.46	11.130%	$79.4135	$79.41	$79.40	$79.40
Purchase #7	$170.89	8.623%	$185.6258	$185.63	$185.65	$185.60
7 purchase totals =	$809.56		$876.4957	$876.51	$876.50	$876.50