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	$31.88	5.753%	$33.7141	$33.71	$33.70	$33.70
Purchase #2	$96.66	9.623%	$105.9616	$105.96	$105.95	$106.00
Purchase #3	$240.78	5.448%	$253.8977	$253.90	$253.90	$253.90
Purchase #4	$123.82	6.329%	$131.6566	$131.66	$131.65	$131.70
Purchase #5	$105.77	10.561%	$116.9404	$116.94	$116.95	$116.90
Purchase #6	$59.48	11.630%	$66.3975	$66.40	$66.40	$66.40
Purchase #7	$195.34	5.745%	$206.5623	$206.56	$206.55	$206.60
7 purchase totals =	$853.73		$915.1302	$915.13	$915.10	$915.20