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	$37.30	9.673%	$40.908	$40.91	$40.90	$40.90
Purchase #2	$210.78	8.130%	$227.9164	$227.92	$227.90	$227.90
Purchase #3	$59.82	11.712%	$66.8261	$66.83	$66.85	$66.80
Purchase #4	$42.88	10.733%	$47.4823	$47.48	$47.50	$47.50
Purchase #5	$81.75	3.378%	$84.5115	$84.51	$84.50	$84.50
Purchase #6	$22.51	7.804%	$24.2667	$24.27	$24.25	$24.30
Purchase #7	$156.59	3.744%	$162.4527	$162.45	$162.45	$162.50
7 purchase totals =	$611.63		$654.3637	$654.37	$654.35	$654.40