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	$120.30	13.187%	$136.164	$136.16	$136.15	$136.20
Purchase #2	$248.96	10.595%	$275.3373	$275.34	$275.35	$275.30
Purchase #3	$36.50	13.377%	$41.3826	$41.38	$41.40	$41.40
Purchase #4	$216.59	11.544%	$241.5931	$241.59	$241.60	$241.60
Purchase #5	$40.71	11.865%	$45.5402	$45.54	$45.55	$45.50
Purchase #6	$44.79	9.840%	$49.1973	$49.20	$49.20	$49.20
Purchase #7	$225.34	8.361%	$244.1807	$244.18	$244.20	$244.20
7 purchase totals =	$933.19		$1,033.3952	$1,033.39	$1,033.45	$1,033.40