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	$41.31	5.873%	$43.7361	$43.74	$43.75	$43.70
Purchase #2	$34.77	6.754%	$37.1184	$37.12	$37.10	$37.10
Purchase #3	$40.83	5.309%	$42.9977	$43.00	$43.00	$43.00
Purchase #4	$49.39	10.105%	$54.3809	$54.38	$54.40	$54.40
Purchase #5	$137.42	6.166%	$145.8933	$145.89	$145.90	$145.90
Purchase #6	$191.47	9.570%	$209.7937	$209.79	$209.80	$209.80
Purchase #7	$33.37	10.300%	$36.8071	$36.81	$36.80	$36.80
7 purchase totals =	$528.56		$570.7272	$570.73	$570.75	$570.70