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	$213.54	11.661%	$238.4409	$238.44	$238.45	$238.40
Purchase #2	$80.87	5.325%	$85.1763	$85.18	$85.20	$85.20
Purchase #3	$135.25	3.424%	$139.881	$139.88	$139.90	$139.90
Purchase #4	$6.89	11.612%	$7.6901	$7.69	$7.70	$7.70
Purchase #5	$87.46	5.191%	$92	$92.00	$92.00	$92.00
Purchase #6	$36.25	12.733%	$40.8657	$40.87	$40.85	$40.90
Purchase #7	$17.79	5.645%	$18.7942	$18.79	$18.80	$18.80
7 purchase totals =	$578.05		$622.8482	$622.85	$622.90	$622.90