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	$39.96	12.334%	$44.8887	$44.89	$44.90	$44.90
Purchase #2	$94.72	7.504%	$101.8278	$101.83	$101.85	$101.80
Purchase #3	$101.50	3.352%	$104.9023	$104.90	$104.90	$104.90
Purchase #4	$248.95	13.358%	$282.2047	$282.20	$282.20	$282.20
Purchase #5	$33.80	13.336%	$38.3076	$38.31	$38.30	$38.30
Purchase #6	$142.72	12.553%	$160.6356	$160.64	$160.65	$160.60
Purchase #7	$227.53	4.800%	$238.4514	$238.45	$238.45	$238.50
7 purchase totals =	$889.18		$971.2181	$971.22	$971.25	$971.20