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	$36.73	13.262%	$41.6011	$41.60	$41.60	$41.60
Purchase #2	$53.65	10.644%	$59.3605	$59.36	$59.35	$59.40
Purchase #3	$139.67	3.364%	$144.3685	$144.37	$144.35	$144.40
Purchase #4	$56.82	9.684%	$62.3224	$62.32	$62.30	$62.30
Purchase #5	$82.93	13.287%	$93.9489	$93.95	$93.95	$93.90
Purchase #6	$87.54	10.259%	$96.5207	$96.52	$96.50	$96.50
Purchase #7	$10.39	3.842%	$10.7892	$10.79	$10.80	$10.80
7 purchase totals =	$467.73		$508.9113	$508.91	$508.85	$508.90