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	$40.38	4.873%	$42.3477	$42.35	$42.35	$42.30
Purchase #2	$78.62	9.158%	$85.82	$85.82	$85.80	$85.80
Purchase #3	$222.47	9.640%	$243.9161	$243.92	$243.90	$243.90
Purchase #4	$227.25	12.849%	$256.4494	$256.45	$256.45	$256.40
Purchase #5	$14.80	6.420%	$15.7502	$15.75	$15.75	$15.80
Purchase #6	$57.61	12.238%	$64.6603	$64.66	$64.65	$64.70
Purchase #7	$237.85	4.633%	$248.8696	$248.87	$248.85	$248.90
7 purchase totals =	$878.98		$957.8133	$957.82	$957.75	$957.80