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	$123.78	4.333%	$129.1434	$129.14	$129.15	$129.10
Purchase #2	$45.35	11.196%	$50.4274	$50.43	$50.45	$50.40
Purchase #3	$168.45	10.183%	$185.6033	$185.60	$185.60	$185.60
Purchase #4	$130.89	8.833%	$142.4515	$142.45	$142.45	$142.50
Purchase #5	$202.75	9.289%	$221.5834	$221.58	$221.60	$221.60
Purchase #6	$15.43	11.136%	$17.1483	$17.15	$17.15	$17.10
Purchase #7	$165.33	12.626%	$186.2046	$186.20	$186.20	$186.20
7 purchase totals =	$851.98		$932.5619	$932.55	$932.60	$932.50