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	$53.85	6.534%	$57.3686	$57.37	$57.35	$57.40
Purchase #2	$205.90	3.768%	$213.6583	$213.66	$213.65	$213.70
Purchase #3	$141.50	7.494%	$152.104	$152.10	$152.10	$152.10
Purchase #4	$73.42	10.763%	$81.3222	$81.32	$81.30	$81.30
Purchase #5	$39.63	6.109%	$42.051	$42.05	$42.05	$42.10
Purchase #6	$220.92	4.770%	$231.4579	$231.46	$231.45	$231.50
Purchase #7	$125.38	11.535%	$139.8426	$139.84	$139.85	$139.80
7 purchase totals =	$860.60		$917.8046	$917.80	$917.75	$917.90