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	$80.26	3.611%	$83.1582	$83.16	$83.15	$83.20
Purchase #2	$47.40	5.636%	$50.0715	$50.07	$50.05	$50.10
Purchase #3	$171.65	7.434%	$184.4105	$184.41	$184.40	$184.40
Purchase #4	$238.33	7.324%	$255.7853	$255.79	$255.80	$255.80
Purchase #5	$63.74	6.449%	$67.8506	$67.85	$67.85	$67.90
Purchase #6	$125.85	13.209%	$142.4735	$142.47	$142.45	$142.50
Purchase #7	$87.72	7.736%	$94.506	$94.51	$94.50	$94.50
7 purchase totals =	$814.95		$878.2556	$878.26	$878.20	$878.40