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	$227.38	13.564%	$258.2218	$258.22	$258.20	$258.20
Purchase #2	$203.88	11.497%	$227.3201	$227.32	$227.30	$227.30
Purchase #3	$145.27	5.480%	$153.2308	$153.23	$153.25	$153.20
Purchase #4	$54.47	13.458%	$61.8006	$61.80	$61.80	$61.80
Purchase #5	$39.83	5.473%	$42.0099	$42.01	$42.00	$42.00
Purchase #6	$81.52	12.703%	$91.8755	$91.88	$91.90	$91.90
Purchase #7	$165.27	4.507%	$172.7187	$172.72	$172.70	$172.70
7 purchase totals =	$917.62		$1,007.1774	$1,007.18	$1,007.15	$1,007.10