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	$199.71	11.838%	$223.3517	$223.35	$223.35	$223.40
Purchase #2	$75.66	3.581%	$78.3694	$78.37	$78.35	$78.40
Purchase #3	$235.27	11.329%	$261.9237	$261.92	$261.90	$261.90
Purchase #4	$5.96	5.472%	$6.2861	$6.29	$6.30	$6.30
Purchase #5	$48.65	3.730%	$50.4646	$50.46	$50.45	$50.50
Purchase #6	$59.60	12.117%	$66.8217	$66.82	$66.80	$66.80
Purchase #7	$207.45	9.792%	$227.7635	$227.76	$227.75	$227.80
7 purchase totals =	$832.30		$914.9807	$914.97	$914.90	$915.10