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	$61.68	8.806%	$67.1115	$67.11	$67.10	$67.10
Purchase #2	$66.35	9.872%	$72.9001	$72.90	$72.90	$72.90
Purchase #3	$18.76	13.735%	$21.3367	$21.34	$21.35	$21.30
Purchase #4	$30.52	11.227%	$33.9465	$33.95	$33.95	$33.90
Purchase #5	$169.79	11.109%	$188.652	$188.65	$188.65	$188.70
Purchase #6	$204.28	8.762%	$222.179	$222.18	$222.20	$222.20
Purchase #7	$107.78	9.210%	$117.7065	$117.71	$117.70	$117.70
7 purchase totals =	$659.16		$723.8323	$723.84	$723.85	$723.80