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	$128.82	8.592%	$139.8882	$139.89	$139.90	$139.90
Purchase #2	$33.94	7.312%	$36.4217	$36.42	$36.40	$36.40
Purchase #3	$32.94	3.671%	$34.1492	$34.15	$34.15	$34.10
Purchase #4	$10.87	7.172%	$11.6496	$11.65	$11.65	$11.60
Purchase #5	$99.90	10.603%	$110.4924	$110.49	$110.50	$110.50
Purchase #6	$187.80	7.287%	$201.485	$201.49	$201.50	$201.50
Purchase #7	$40.96	3.598%	$42.4337	$42.43	$42.45	$42.40
7 purchase totals =	$535.23		$576.5198	$576.52	$576.55	$576.40