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	$90.42	8.703%	$98.2893	$98.29	$98.30	$98.30
Purchase #2	$47.78	6.141%	$50.7142	$50.71	$50.70	$50.70
Purchase #3	$152.74	12.768%	$172.2418	$172.24	$172.25	$172.20
Purchase #4	$122.51	3.853%	$127.2303	$127.23	$127.25	$127.20
Purchase #5	$211.90	13.405%	$240.3052	$240.31	$240.30	$240.30
Purchase #6	$101.61	8.707%	$110.4572	$110.46	$110.45	$110.50
Purchase #7	$55.59	9.677%	$60.9694	$60.97	$60.95	$61.00
7 purchase totals =	$782.55		$860.2074	$860.21	$860.20	$860.20