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	$212.94	5.836%	$225.3672	$225.37	$225.35	$225.40
Purchase #2	$15.52	10.379%	$17.1308	$17.13	$17.15	$17.10
Purchase #3	$120.33	5.564%	$127.0252	$127.03	$127.05	$127.00
Purchase #4	$119.35	10.173%	$131.4915	$131.49	$131.50	$131.50
Purchase #5	$127.49	6.369%	$135.6098	$135.61	$135.60	$135.60
Purchase #6	$145.90	13.811%	$166.0502	$166.05	$166.05	$166.10
Purchase #7	$17.61	3.441%	$18.216	$18.22	$18.20	$18.20
7 purchase totals =	$759.14		$820.8907	$820.90	$820.90	$820.90