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	$178.58	6.502%	$190.1913	$190.19	$190.20	$190.20
Purchase #2	$75.82	9.242%	$82.8273	$82.83	$82.85	$82.80
Purchase #3	$221.61	13.645%	$251.8487	$251.85	$251.85	$251.80
Purchase #4	$157.80	9.617%	$172.9756	$172.98	$173.00	$173.00
Purchase #5	$128.42	10.132%	$141.4315	$141.43	$141.45	$141.40
Purchase #6	$101.97	8.408%	$110.5436	$110.54	$110.55	$110.50
Purchase #7	$154.34	3.262%	$159.3746	$159.37	$159.35	$159.40
7 purchase totals =	$1,018.54		$1,109.1926	$1,109.19	$1,109.25	$1,109.10