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	$80.78	11.275%	$89.8879	$89.89	$89.90	$89.90
Purchase #2	$104.76	7.586%	$112.7071	$112.71	$112.70	$112.70
Purchase #3	$62.83	7.665%	$67.6459	$67.65	$67.65	$67.60
Purchase #4	$159.83	6.843%	$170.7672	$170.77	$170.75	$170.80
Purchase #5	$235.29	5.105%	$247.3016	$247.30	$247.30	$247.30
Purchase #6	$125.59	10.647%	$138.9616	$138.96	$138.95	$139.00
Purchase #7	$117.93	7.249%	$126.4787	$126.48	$126.50	$126.50
7 purchase totals =	$887.01		$953.7500	$953.76	$953.75	$953.80