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	$120.49	13.186%	$136.3778	$136.38	$136.40	$136.40
Purchase #2	$165.88	13.266%	$187.8856	$187.89	$187.90	$187.90
Purchase #3	$153.50	12.499%	$172.686	$172.69	$172.70	$172.70
Purchase #4	$59.25	7.848%	$63.8999	$63.90	$63.90	$63.90
Purchase #5	$229.49	11.714%	$256.3725	$256.37	$256.35	$256.40
Purchase #6	$33.52	8.587%	$36.3984	$36.40	$36.40	$36.40
Purchase #7	$131.67	13.856%	$149.9142	$149.91	$149.90	$149.90
7 purchase totals =	$893.80		$1,003.5344	$1,003.54	$1,003.55	$1,003.60