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	$218.88	12.313%	$245.8307	$245.83	$245.85	$245.80
Purchase #2	$94.69	11.427%	$105.5102	$105.51	$105.50	$105.50
Purchase #3	$67.89	5.340%	$71.5153	$71.52	$71.50	$71.50
Purchase #4	$124.53	3.534%	$128.9309	$128.93	$128.95	$128.90
Purchase #5	$153.89	5.130%	$161.7846	$161.78	$161.80	$161.80
Purchase #6	$87.54	3.571%	$90.6661	$90.67	$90.65	$90.70
Purchase #7	$31.60	6.242%	$33.5725	$33.57	$33.55	$33.60
7 purchase totals =	$779.02		$837.8103	$837.81	$837.80	$837.80