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	$83.71	9.361%	$91.5461	$91.55	$91.55	$91.50
Purchase #2	$64.69	10.109%	$71.2295	$71.23	$71.25	$71.20
Purchase #3	$227.26	10.106%	$250.2269	$250.23	$250.25	$250.20
Purchase #4	$106.42	13.492%	$120.7782	$120.78	$120.80	$120.80
Purchase #5	$246.51	8.151%	$266.603	$266.60	$266.60	$266.60
Purchase #6	$148.33	4.823%	$155.484	$155.48	$155.50	$155.50
Purchase #7	$94.48	9.554%	$103.5066	$103.51	$103.50	$103.50
7 purchase totals =	$971.40		$1,059.3743	$1,059.38	$1,059.45	$1,059.30