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	$228.74	13.189%	$258.9085	$258.91	$258.90	$258.90
Purchase #2	$197.59	12.571%	$222.429	$222.43	$222.45	$222.40
Purchase #3	$49.67	12.361%	$55.8097	$55.81	$55.80	$55.80
Purchase #4	$191.25	4.814%	$200.4568	$200.46	$200.45	$200.50
Purchase #5	$218.53	7.151%	$234.1571	$234.16	$234.15	$234.20
Purchase #6	$91.55	3.430%	$94.6902	$94.69	$94.70	$94.70
Purchase #7	$204.31	11.583%	$227.9752	$227.98	$228.00	$228.00
7 purchase totals =	$1,181.64		$1,294.4265	$1,294.44	$1,294.45	$1,294.50