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	$139.63	8.795%	$151.9105	$151.91	$151.90	$151.90
Purchase #2	$184.89	13.622%	$210.0757	$210.08	$210.10	$210.10
Purchase #3	$159.42	12.147%	$178.7847	$178.78	$178.80	$178.80
Purchase #4	$104.79	12.389%	$117.7724	$117.77	$117.75	$117.80
Purchase #5	$73.53	13.740%	$83.633	$83.63	$83.65	$83.60
Purchase #6	$165.90	8.704%	$180.3399	$180.34	$180.35	$180.30
Purchase #7	$82.82	13.847%	$94.2881	$94.29	$94.30	$94.30
7 purchase totals =	$910.98		$1,016.8043	$1,016.80	$1,016.85	$1,016.80