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	$222.34	8.138%	$240.434	$240.43	$240.45	$240.40
Purchase #2	$115.86	9.660%	$127.0521	$127.05	$127.05	$127.10
Purchase #3	$145.58	13.473%	$165.194	$165.19	$165.20	$165.20
Purchase #4	$155.62	10.644%	$172.1842	$172.18	$172.20	$172.20
Purchase #5	$43.89	13.285%	$49.7208	$49.72	$49.70	$49.70
Purchase #6	$36.90	5.217%	$38.8251	$38.83	$38.85	$38.80
Purchase #7	$244.62	9.703%	$268.3555	$268.36	$268.35	$268.40
7 purchase totals =	$964.81		$1,061.7657	$1,061.76	$1,061.80	$1,061.80