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	$119.48	10.424%	$131.9346	$131.93	$131.95	$131.90
Purchase #2	$87.50	3.741%	$90.7734	$90.77	$90.75	$90.80
Purchase #3	$33.79	13.639%	$38.3986	$38.40	$38.40	$38.40
Purchase #4	$138.90	8.157%	$150.2301	$150.23	$150.25	$150.20
Purchase #5	$172.75	10.351%	$190.6314	$190.63	$190.65	$190.60
Purchase #6	$180.47	4.410%	$188.4287	$188.43	$188.45	$188.40
Purchase #7	$36.84	4.484%	$38.4919	$38.49	$38.50	$38.50
7 purchase totals =	$769.73		$828.8887	$828.88	$828.95	$828.80