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	$172.49	6.803%	$184.2245	$184.22	$184.20	$184.20
Purchase #2	$216.78	3.566%	$224.5104	$224.51	$224.50	$224.50
Purchase #3	$29.43	12.634%	$33.1482	$33.15	$33.15	$33.10
Purchase #4	$72.88	7.791%	$78.5581	$78.56	$78.55	$78.60
Purchase #5	$137.48	5.111%	$144.5066	$144.51	$144.50	$144.50
Purchase #6	$243.73	12.814%	$274.9616	$274.96	$274.95	$275.00
Purchase #7	$111.62	4.195%	$116.3025	$116.30	$116.30	$116.30
7 purchase totals =	$984.41		$1,056.2119	$1,056.21	$1,056.15	$1,056.20