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	$34.74	6.768%	$37.0912	$37.09	$37.10	$37.10
Purchase #2	$194.86	13.851%	$221.8501	$221.85	$221.85	$221.90
Purchase #3	$199.42	5.137%	$209.6642	$209.66	$209.65	$209.70
Purchase #4	$242.90	3.688%	$251.8582	$251.86	$251.85	$251.90
Purchase #5	$117.49	11.581%	$131.0965	$131.10	$131.10	$131.10
Purchase #6	$127.92	9.188%	$139.6733	$139.67	$139.65	$139.70
Purchase #7	$95.83	4.864%	$100.4912	$100.49	$100.50	$100.50
7 purchase totals =	$1,013.16		$1,091.7247	$1,091.72	$1,091.70	$1,091.90