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	$157.49	5.123%	$165.5582	$165.56	$165.55	$165.60
Purchase #2	$154.76	8.770%	$168.3325	$168.33	$168.35	$168.30
Purchase #3	$68.79	13.405%	$78.0113	$78.01	$78.00	$78.00
Purchase #4	$93.68	13.575%	$106.3971	$106.40	$106.40	$106.40
Purchase #5	$37.31	8.661%	$40.5414	$40.54	$40.55	$40.50
Purchase #6	$158.36	4.697%	$165.7982	$165.80	$165.80	$165.80
Purchase #7	$73.77	10.583%	$81.5771	$81.58	$81.60	$81.60
7 purchase totals =	$744.16		$806.2158	$806.22	$806.25	$806.20