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	$67.36	7.624%	$72.4955	$72.50	$72.50	$72.50
Purchase #2	$84.81	4.568%	$88.6841	$88.68	$88.70	$88.70
Purchase #3	$100.55	7.231%	$107.8208	$107.82	$107.80	$107.80
Purchase #4	$117.88	10.827%	$130.6429	$130.64	$130.65	$130.60
Purchase #5	$12.64	6.177%	$13.4208	$13.42	$13.40	$13.40
Purchase #6	$209.62	7.754%	$225.8739	$225.87	$225.85	$225.90
Purchase #7	$26.52	7.472%	$28.5016	$28.50	$28.50	$28.50
7 purchase totals =	$619.38		$667.4396	$667.43	$667.40	$667.40