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	$87.94	8.340%	$95.2742	$95.27	$95.25	$95.30
Purchase #2	$200.68	13.252%	$227.2741	$227.27	$227.25	$227.30
Purchase #3	$95.90	3.504%	$99.2603	$99.26	$99.25	$99.30
Purchase #4	$64.89	4.645%	$67.9041	$67.90	$67.90	$67.90
Purchase #5	$56.49	6.113%	$59.9432	$59.94	$59.95	$59.90
Purchase #6	$32.34	4.186%	$33.6938	$33.69	$33.70	$33.70
Purchase #7	$249.37	10.428%	$275.3743	$275.37	$275.35	$275.40
7 purchase totals =	$787.61		$858.7240	$858.70	$858.65	$858.80