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	$220.65	13.320%	$250.0406	$250.04	$250.05	$250.00
Purchase #2	$37.59	9.309%	$41.0893	$41.09	$41.10	$41.10
Purchase #3	$81.71	9.340%	$89.3417	$89.34	$89.35	$89.30
Purchase #4	$37.62	13.857%	$42.833	$42.83	$42.85	$42.80
Purchase #5	$141.35	11.738%	$157.9417	$157.94	$157.95	$157.90
Purchase #6	$44.67	4.847%	$46.8352	$46.84	$46.85	$46.80
Purchase #7	$71.67	10.381%	$79.1101	$79.11	$79.10	$79.10
7 purchase totals =	$635.26		$707.1916	$707.19	$707.25	$707.00