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	$18.91	4.825%	$19.8224	$19.82	$19.80	$19.80
Purchase #2	$75.94	5.110%	$79.8205	$79.82	$79.80	$79.80
Purchase #3	$137.56	8.236%	$148.8894	$148.89	$148.90	$148.90
Purchase #4	$182.82	6.811%	$195.2719	$195.27	$195.25	$195.30
Purchase #5	$138.36	13.840%	$157.509	$157.51	$157.50	$157.50
Purchase #6	$50.51	6.352%	$53.7184	$53.72	$53.70	$53.70
Purchase #7	$81.64	9.367%	$89.2872	$89.29	$89.30	$89.30
7 purchase totals =	$685.74		$744.3188	$744.32	$744.25	$744.30