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	$102.31	8.715%	$111.2263	$111.23	$111.25	$111.20
Purchase #2	$223.32	6.666%	$238.2065	$238.21	$238.20	$238.20
Purchase #3	$26.78	5.117%	$28.1503	$28.15	$28.15	$28.20
Purchase #4	$85.77	6.437%	$91.291	$91.29	$91.30	$91.30
Purchase #5	$47.38	11.524%	$52.8401	$52.84	$52.85	$52.80
Purchase #6	$71.62	6.603%	$76.3491	$76.35	$76.35	$76.30
Purchase #7	$60.40	7.551%	$64.9608	$64.96	$64.95	$65.00
7 purchase totals =	$617.58		$663.0241	$663.03	$663.05	$663.00