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	$50.61	13.619%	$57.5026	$57.50	$57.50	$57.50
Purchase #2	$183.93	6.222%	$195.3741	$195.37	$195.35	$195.40
Purchase #3	$222.75	9.197%	$243.2363	$243.24	$243.25	$243.20
Purchase #4	$126.39	12.180%	$141.7843	$141.78	$141.80	$141.80
Purchase #5	$80.67	9.726%	$88.516	$88.52	$88.50	$88.50
Purchase #6	$144.66	11.323%	$161.0399	$161.04	$161.05	$161.00
Purchase #7	$187.44	13.583%	$212.9	$212.90	$212.90	$212.90
7 purchase totals =	$996.45		$1,100.3532	$1,100.35	$1,100.35	$1,100.30