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	$236.94	4.172%	$246.8251	$246.83	$246.85	$246.80
Purchase #2	$241.93	12.445%	$272.0382	$272.04	$272.05	$272.00
Purchase #3	$125.74	10.853%	$139.3866	$139.39	$139.40	$139.40
Purchase #4	$48.39	5.223%	$50.9174	$50.92	$50.90	$50.90
Purchase #5	$27.50	4.577%	$28.7587	$28.76	$28.75	$28.80
Purchase #6	$88.32	12.475%	$99.3379	$99.34	$99.35	$99.30
Purchase #7	$105.34	10.725%	$116.6377	$116.64	$116.65	$116.60
7 purchase totals =	$874.16		$953.9016	$953.92	$953.95	$953.80