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	$39.28	11.303%	$43.7198	$43.72	$43.70	$43.70
Purchase #2	$167.31	10.779%	$185.3443	$185.34	$185.35	$185.30
Purchase #3	$137.33	10.599%	$151.8856	$151.89	$151.90	$151.90
Purchase #4	$114.94	5.424%	$121.1743	$121.17	$121.15	$121.20
Purchase #5	$100.56	7.343%	$107.9441	$107.94	$107.95	$107.90
Purchase #6	$84.68	5.105%	$89.0029	$89.00	$89.00	$89.00
Purchase #7	$87.67	7.563%	$94.3005	$94.30	$94.30	$94.30
7 purchase totals =	$731.77		$793.3715	$793.36	$793.35	$793.30