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	$118.72	10.797%	$131.5382	$131.54	$131.55	$131.50
Purchase #2	$70.43	10.557%	$77.8653	$77.87	$77.85	$77.90
Purchase #3	$48.74	12.673%	$54.9168	$54.92	$54.90	$54.90
Purchase #4	$77.62	10.371%	$85.67	$85.67	$85.65	$85.70
Purchase #5	$146.32	8.140%	$158.2304	$158.23	$158.25	$158.20
Purchase #6	$203.32	8.588%	$220.7811	$220.78	$220.80	$220.80
Purchase #7	$37.50	5.378%	$39.5168	$39.52	$39.50	$39.50
7 purchase totals =	$702.65		$768.5186	$768.53	$768.50	$768.50