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	$246.47	5.554%	$260.1589	$260.16	$260.15	$260.20
Purchase #2	$227.50	8.278%	$246.3325	$246.33	$246.35	$246.30
Purchase #3	$245.37	4.119%	$255.4768	$255.48	$255.50	$255.50
Purchase #4	$113.86	12.253%	$127.8113	$127.81	$127.80	$127.80
Purchase #5	$126.34	10.678%	$139.8306	$139.83	$139.85	$139.80
Purchase #6	$84.42	3.528%	$87.3983	$87.40	$87.40	$87.40
Purchase #7	$209.76	3.181%	$216.4325	$216.43	$216.45	$216.40
7 purchase totals =	$1,253.72		$1,333.4409	$1,333.44	$1,333.50	$1,333.40