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	$85.63	5.291%	$90.1607	$90.16	$90.15	$90.20
Purchase #2	$156.80	13.164%	$177.4412	$177.44	$177.45	$177.40
Purchase #3	$66.57	10.103%	$73.2956	$73.30	$73.30	$73.30
Purchase #4	$15.77	4.855%	$16.5356	$16.54	$16.55	$16.50
Purchase #5	$204.79	9.144%	$223.516	$223.52	$223.50	$223.50
Purchase #6	$72.49	8.644%	$78.756	$78.76	$78.75	$78.80
Purchase #7	$40.26	3.123%	$41.5173	$41.52	$41.50	$41.50
7 purchase totals =	$642.31		$701.2224	$701.24	$701.20	$701.20