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	$92.83	11.606%	$103.6038	$103.60	$103.60	$103.60
Purchase #2	$157.78	9.138%	$172.1979	$172.20	$172.20	$172.20
Purchase #3	$135.57	12.745%	$152.8484	$152.85	$152.85	$152.80
Purchase #4	$218.99	5.498%	$231.0301	$231.03	$231.05	$231.00
Purchase #5	$116.57	5.526%	$123.0117	$123.01	$123.00	$123.00
Purchase #6	$61.98	13.569%	$70.3901	$70.39	$70.40	$70.40
Purchase #7	$47.91	5.300%	$50.4492	$50.45	$50.45	$50.40
7 purchase totals =	$831.63		$903.5312	$903.53	$903.55	$903.40