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	$249.53	10.398%	$275.4761	$275.48	$275.50	$275.50
Purchase #2	$240.68	12.769%	$271.4124	$271.41	$271.40	$271.40
Purchase #3	$200.52	8.782%	$218.1297	$218.13	$218.15	$218.10
Purchase #4	$138.79	7.186%	$148.7634	$148.76	$148.75	$148.80
Purchase #5	$36.60	11.478%	$40.8009	$40.80	$40.80	$40.80
Purchase #6	$37.97	7.442%	$40.7957	$40.80	$40.80	$40.80
Purchase #7	$132.90	13.791%	$151.2282	$151.23	$151.25	$151.20
7 purchase totals =	$1,036.99		$1,146.6064	$1,146.61	$1,146.65	$1,146.60