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	$239.67	13.103%	$271.074	$271.07	$271.05	$271.10
Purchase #2	$159.25	4.624%	$166.6137	$166.61	$166.60	$166.60
Purchase #3	$56.35	11.856%	$63.0309	$63.03	$63.05	$63.00
Purchase #4	$140.50	3.121%	$144.885	$144.89	$144.90	$144.90
Purchase #5	$16.89	7.151%	$18.0978	$18.10	$18.10	$18.10
Purchase #6	$171.88	4.171%	$179.0491	$179.05	$179.05	$179.00
Purchase #7	$41.88	8.858%	$45.5897	$45.59	$45.60	$45.60
7 purchase totals =	$826.42		$888.3402	$888.34	$888.35	$888.30