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	$147.63	12.201%	$165.6423	$165.64	$165.65	$165.60
Purchase #2	$117.69	7.758%	$126.8204	$126.82	$126.80	$126.80
Purchase #3	$213.74	4.134%	$222.576	$222.58	$222.60	$222.60
Purchase #4	$233.63	11.597%	$260.7241	$260.72	$260.70	$260.70
Purchase #5	$40.28	6.429%	$42.8696	$42.87	$42.85	$42.90
Purchase #6	$198.28	6.198%	$210.5694	$210.57	$210.55	$210.60
Purchase #7	$38.84	12.418%	$43.6632	$43.66	$43.65	$43.70
7 purchase totals =	$990.09		$1,072.8650	$1,072.86	$1,072.80	$1,072.90