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	$64.25	13.293%	$72.7908	$72.79	$72.80	$72.80
Purchase #2	$77.58	10.209%	$85.5001	$85.50	$85.50	$85.50
Purchase #3	$92.31	8.508%	$100.1637	$100.16	$100.15	$100.20
Purchase #4	$209.85	13.697%	$238.5932	$238.59	$238.60	$238.60
Purchase #5	$168.78	11.484%	$188.1627	$188.16	$188.15	$188.20
Purchase #6	$20.53	13.262%	$23.2527	$23.25	$23.25	$23.30
Purchase #7	$99.89	3.200%	$103.0865	$103.09	$103.10	$103.10
7 purchase totals =	$733.19		$811.5497	$811.54	$811.55	$811.70