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	$192.31	12.286%	$215.9372	$215.94	$215.95	$215.90
Purchase #2	$47.81	3.376%	$49.4241	$49.42	$49.40	$49.40
Purchase #3	$97.78	5.871%	$103.5207	$103.52	$103.50	$103.50
Purchase #4	$89.47	10.192%	$98.5888	$98.59	$98.60	$98.60
Purchase #5	$213.95	8.194%	$231.4811	$231.48	$231.50	$231.50
Purchase #6	$18.44	11.468%	$20.5547	$20.55	$20.55	$20.60
Purchase #7	$189.60	3.627%	$196.4768	$196.48	$196.50	$196.50
7 purchase totals =	$849.36		$915.9834	$915.98	$916.00	$916.00