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	$91.82	12.813%	$103.5849	$103.58	$103.60	$103.60
Purchase #2	$38.83	3.479%	$40.1809	$40.18	$40.20	$40.20
Purchase #3	$151.26	12.756%	$170.5547	$170.55	$170.55	$170.60
Purchase #4	$6.81	9.776%	$7.4757	$7.48	$7.50	$7.50
Purchase #5	$82.94	9.787%	$91.0573	$91.06	$91.05	$91.10
Purchase #6	$246.66	12.761%	$278.1363	$278.14	$278.15	$278.10
Purchase #7	$95.73	8.468%	$103.8364	$103.84	$103.85	$103.80
7 purchase totals =	$714.05		$794.8262	$794.83	$794.90	$794.90