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	$159.46	13.520%	$181.019	$181.02	$181.00	$181.00
Purchase #2	$238.52	5.169%	$250.8491	$250.85	$250.85	$250.80
Purchase #3	$61.98	4.565%	$64.8094	$64.81	$64.80	$64.80
Purchase #4	$61.46	9.534%	$67.3196	$67.32	$67.30	$67.30
Purchase #5	$242.39	5.703%	$256.2135	$256.21	$256.20	$256.20
Purchase #6	$72.58	12.216%	$81.4464	$81.45	$81.45	$81.40
Purchase #7	$35.29	11.858%	$39.4747	$39.47	$39.45	$39.50
7 purchase totals =	$871.68		$941.1317	$941.13	$941.05	$941.00