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	$56.81	5.103%	$59.709	$59.71	$59.70	$59.70
Purchase #2	$131.47	6.750%	$140.3442	$140.34	$140.35	$140.30
Purchase #3	$124.66	5.654%	$131.7083	$131.71	$131.70	$131.70
Purchase #4	$77.30	10.360%	$85.3083	$85.31	$85.30	$85.30
Purchase #5	$186.66	5.126%	$196.2282	$196.23	$196.25	$196.20
Purchase #6	$93.51	4.772%	$97.9723	$97.97	$97.95	$98.00
Purchase #7	$222.34	6.536%	$236.8721	$236.87	$236.85	$236.90
7 purchase totals =	$892.75		$948.1424	$948.14	$948.10	$948.10