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	$169.55	12.401%	$190.5759	$190.58	$190.60	$190.60
Purchase #2	$204.64	11.519%	$228.2125	$228.21	$228.20	$228.20
Purchase #3	$237.41	11.484%	$264.6742	$264.67	$264.65	$264.70
Purchase #4	$61.48	6.601%	$65.5383	$65.54	$65.55	$65.50
Purchase #5	$13.96	11.830%	$15.6115	$15.61	$15.60	$15.60
Purchase #6	$177.52	8.208%	$192.0908	$192.09	$192.10	$192.10
Purchase #7	$75.93	9.148%	$82.8761	$82.88	$82.90	$82.90
7 purchase totals =	$940.49		$1,039.5793	$1,039.58	$1,039.60	$1,039.60