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	$159.26	7.514%	$171.2268	$171.23	$171.25	$171.20
Purchase #2	$152.57	10.433%	$168.4876	$168.49	$168.50	$168.50
Purchase #3	$120.45	9.512%	$131.9072	$131.91	$131.90	$131.90
Purchase #4	$12.63	10.192%	$13.9172	$13.92	$13.90	$13.90
Purchase #5	$110.55	12.232%	$124.0725	$124.07	$124.05	$124.10
Purchase #6	$194.46	3.140%	$200.566	$200.57	$200.55	$200.60
Purchase #7	$78.85	12.447%	$88.6645	$88.66	$88.65	$88.70
7 purchase totals =	$828.77		$898.8418	$898.85	$898.80	$898.90