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	$242.71	11.846%	$271.4614	$271.46	$271.45	$271.50
Purchase #2	$139.71	3.507%	$144.6096	$144.61	$144.60	$144.60
Purchase #3	$138.78	4.335%	$144.7961	$144.80	$144.80	$144.80
Purchase #4	$126.68	11.768%	$141.5877	$141.59	$141.60	$141.60
Purchase #5	$48.84	9.499%	$53.4793	$53.48	$53.50	$53.50
Purchase #6	$236.92	4.609%	$247.8396	$247.84	$247.85	$247.80
Purchase #7	$15.90	3.676%	$16.4845	$16.48	$16.50	$16.50
7 purchase totals =	$949.54		$1,020.2582	$1,020.26	$1,020.30	$1,020.30