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	$203.70	11.846%	$227.8303	$227.83	$227.85	$227.80
Purchase #2	$189.51	4.495%	$198.0285	$198.03	$198.05	$198.00
Purchase #3	$102.80	5.856%	$108.82	$108.82	$108.80	$108.80
Purchase #4	$165.71	9.130%	$180.8393	$180.84	$180.85	$180.80
Purchase #5	$171.31	5.823%	$181.2854	$181.29	$181.30	$181.30
Purchase #6	$153.82	3.762%	$159.6067	$159.61	$159.60	$159.60
Purchase #7	$22.74	8.667%	$24.7109	$24.71	$24.70	$24.70
7 purchase totals =	$1,009.59		$1,081.1211	$1,081.13	$1,081.15	$1,081.00