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	$134.95	3.619%	$139.8338	$139.83	$139.85	$139.80
Purchase #2	$214.34	9.507%	$234.7173	$234.72	$234.70	$234.70
Purchase #3	$181.40	10.620%	$200.6647	$200.66	$200.65	$200.70
Purchase #4	$46.53	13.462%	$52.7939	$52.79	$52.80	$52.80
Purchase #5	$229.83	13.110%	$259.9607	$259.96	$259.95	$260.00
Purchase #6	$21.35	13.447%	$24.2209	$24.22	$24.20	$24.20
Purchase #7	$123.61	3.529%	$127.9722	$127.97	$127.95	$128.00
7 purchase totals =	$952.01		$1,040.1635	$1,040.15	$1,040.10	$1,040.20