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	$67.48	6.867%	$72.1139	$72.11	$72.10	$72.10
Purchase #2	$221.65	12.471%	$249.292	$249.29	$249.30	$249.30
Purchase #3	$107.76	4.481%	$112.5887	$112.59	$112.60	$112.60
Purchase #4	$27.78	11.526%	$30.9819	$30.98	$31.00	$31.00
Purchase #5	$124.72	4.293%	$130.0742	$130.07	$130.05	$130.10
Purchase #6	$99.47	5.694%	$105.1338	$105.13	$105.15	$105.10
Purchase #7	$197.31	10.190%	$217.4159	$217.42	$217.40	$217.40
7 purchase totals =	$846.17		$917.6004	$917.59	$917.60	$917.60