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	$137.28	10.411%	$151.5722	$151.57	$151.55	$151.60
Purchase #2	$219.92	10.170%	$242.2859	$242.29	$242.30	$242.30
Purchase #3	$76.83	12.675%	$86.5682	$86.57	$86.55	$86.60
Purchase #4	$92.55	12.299%	$103.9327	$103.93	$103.95	$103.90
Purchase #5	$69.83	5.394%	$73.5966	$73.60	$73.60	$73.60
Purchase #6	$61.26	3.574%	$63.4494	$63.45	$63.45	$63.40
Purchase #7	$81.56	12.222%	$91.5283	$91.53	$91.55	$91.50
7 purchase totals =	$739.23		$812.9333	$812.94	$812.95	$812.90