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	$239.26	3.381%	$247.3494	$247.35	$247.35	$247.30
Purchase #2	$101.82	9.191%	$111.1783	$111.18	$111.20	$111.20
Purchase #3	$54.47	13.659%	$61.9101	$61.91	$61.90	$61.90
Purchase #4	$127.66	13.600%	$145.0218	$145.02	$145.00	$145.00
Purchase #5	$122.35	6.802%	$130.6722	$130.67	$130.65	$130.70
Purchase #6	$170.91	8.837%	$186.0133	$186.01	$186.00	$186.00
Purchase #7	$17.77	5.741%	$18.7902	$18.79	$18.80	$18.80
7 purchase totals =	$834.24		$900.9353	$900.93	$900.90	$900.90