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	$129.97	8.677%	$141.2475	$141.25	$141.25	$141.20
Purchase #2	$36.61	6.796%	$39.098	$39.10	$39.10	$39.10
Purchase #3	$76.60	12.485%	$86.1635	$86.16	$86.15	$86.20
Purchase #4	$13.85	11.328%	$15.4189	$15.42	$15.40	$15.40
Purchase #5	$56.62	8.527%	$61.448	$61.45	$61.45	$61.40
Purchase #6	$151.81	13.275%	$171.9628	$171.96	$171.95	$172.00
Purchase #7	$136.31	13.606%	$154.8563	$154.86	$154.85	$154.90
7 purchase totals =	$601.77		$670.1950	$670.20	$670.15	$670.20