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	$238.59	3.614%	$247.2126	$247.21	$247.20	$247.20
Purchase #2	$40.50	8.501%	$43.9429	$43.94	$43.95	$43.90
Purchase #3	$182.32	10.143%	$200.8127	$200.81	$200.80	$200.80
Purchase #4	$92.68	12.553%	$104.3141	$104.31	$104.30	$104.30
Purchase #5	$228.38	13.366%	$258.9053	$258.91	$258.90	$258.90
Purchase #6	$239.53	3.510%	$247.9375	$247.94	$247.95	$247.90
Purchase #7	$142.45	5.859%	$150.7961	$150.80	$150.80	$150.80
7 purchase totals =	$1,164.45		$1,253.9212	$1,253.92	$1,253.90	$1,253.80