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	$61.92	6.649%	$66.0371	$66.04	$66.05	$66.00
Purchase #2	$153.71	11.257%	$171.0131	$171.01	$171.00	$171.00
Purchase #3	$15.33	3.832%	$15.9174	$15.92	$15.90	$15.90
Purchase #4	$140.85	3.171%	$145.3164	$145.32	$145.30	$145.30
Purchase #5	$173.38	13.592%	$196.9458	$196.95	$196.95	$196.90
Purchase #6	$158.33	9.145%	$172.8093	$172.81	$172.80	$172.80
Purchase #7	$131.35	3.710%	$136.2231	$136.22	$136.20	$136.20
7 purchase totals =	$834.87		$904.2622	$904.27	$904.20	$904.10