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	$75.47	8.414%	$81.82	$81.82	$81.80	$81.80
Purchase #2	$159.87	11.560%	$178.351	$178.35	$178.35	$178.40
Purchase #3	$122.66	7.403%	$131.7405	$131.74	$131.75	$131.70
Purchase #4	$106.85	4.453%	$111.608	$111.61	$111.60	$111.60
Purchase #5	$250.64	6.733%	$267.5156	$267.52	$267.50	$267.50
Purchase #6	$75.78	13.219%	$85.7974	$85.80	$85.80	$85.80
Purchase #7	$57.77	6.816%	$61.7076	$61.71	$61.70	$61.70
7 purchase totals =	$849.04		$918.5401	$918.55	$918.50	$918.50