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	$125.83	10.802%	$139.4222	$139.42	$139.40	$139.40
Purchase #2	$203.90	8.726%	$221.6923	$221.69	$221.70	$221.70
Purchase #3	$120.74	13.493%	$137.0314	$137.03	$137.05	$137.00
Purchase #4	$216.57	3.711%	$224.6069	$224.61	$224.60	$224.60
Purchase #5	$86.31	3.180%	$89.0547	$89.05	$89.05	$89.10
Purchase #6	$154.44	4.373%	$161.1937	$161.19	$161.20	$161.20
Purchase #7	$137.43	12.434%	$154.518	$154.52	$154.50	$154.50
7 purchase totals =	$1,045.22		$1,127.5192	$1,127.51	$1,127.50	$1,127.50