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	$139.80	13.650%	$158.8827	$158.88	$158.90	$158.90
Purchase #2	$70.72	11.589%	$78.9157	$78.92	$78.90	$78.90
Purchase #3	$214.89	4.857%	$225.3272	$225.33	$225.35	$225.30
Purchase #4	$217.73	9.169%	$237.6937	$237.69	$237.70	$237.70
Purchase #5	$155.78	11.865%	$174.2633	$174.26	$174.25	$174.30
Purchase #6	$43.66	6.849%	$46.6503	$46.65	$46.65	$46.70
Purchase #7	$33.92	4.651%	$35.4976	$35.50	$35.50	$35.50
7 purchase totals =	$876.50		$957.2305	$957.23	$957.25	$957.30