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	$19.60	8.558%	$21.2774	$21.28	$21.30	$21.30
Purchase #2	$39.59	4.756%	$41.4729	$41.47	$41.45	$41.50
Purchase #3	$85.78	4.529%	$89.665	$89.67	$89.65	$89.70
Purchase #4	$209.43	12.484%	$235.5752	$235.58	$235.60	$235.60
Purchase #5	$37.98	4.153%	$39.5573	$39.56	$39.55	$39.60
Purchase #6	$15.47	7.219%	$16.5868	$16.59	$16.60	$16.60
Purchase #7	$238.80	3.499%	$247.1556	$247.16	$247.15	$247.20
7 purchase totals =	$646.65		$691.2902	$691.31	$691.30	$691.50