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	$245.31	11.801%	$274.259	$274.26	$274.25	$274.30
Purchase #2	$91.96	7.235%	$98.6133	$98.61	$98.60	$98.60
Purchase #3	$131.49	9.477%	$143.9513	$143.95	$143.95	$144.00
Purchase #4	$29.60	12.637%	$33.3406	$33.34	$33.35	$33.30
Purchase #5	$34.92	7.680%	$37.6019	$37.60	$37.60	$37.60
Purchase #6	$51.29	7.649%	$55.2132	$55.21	$55.20	$55.20
Purchase #7	$172.99	13.682%	$196.6585	$196.66	$196.65	$196.70
7 purchase totals =	$757.56		$839.6378	$839.63	$839.60	$839.70