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	$94.71	6.134%	$100.5195	$100.52	$100.50	$100.50
Purchase #2	$90.81	13.253%	$102.845	$102.85	$102.85	$102.80
Purchase #3	$23.74	6.220%	$25.2166	$25.22	$25.20	$25.20
Purchase #4	$236.97	9.231%	$258.8447	$258.84	$258.85	$258.80
Purchase #5	$219.27	3.610%	$227.1856	$227.19	$227.20	$227.20
Purchase #6	$199.25	11.802%	$222.7655	$222.77	$222.75	$222.80
Purchase #7	$205.56	8.375%	$222.7757	$222.78	$222.80	$222.80
7 purchase totals =	$1,070.31		$1,160.1526	$1,160.17	$1,160.15	$1,160.10