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	$55.99	6.644%	$59.71	$59.71	$59.70	$59.70
Purchase #2	$183.64	13.633%	$208.6756	$208.68	$208.70	$208.70
Purchase #3	$215.62	4.618%	$225.5773	$225.58	$225.60	$225.60
Purchase #4	$47.50	6.263%	$50.4749	$50.47	$50.45	$50.50
Purchase #5	$32.33	10.865%	$35.8427	$35.84	$35.85	$35.80
Purchase #6	$82.82	9.414%	$90.6167	$90.62	$90.60	$90.60
Purchase #7	$218.28	8.340%	$236.4846	$236.48	$236.50	$236.50
7 purchase totals =	$836.18		$907.3818	$907.38	$907.40	$907.40