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	$126.35	9.189%	$137.9603	$137.96	$137.95	$138.00
Purchase #2	$31.25	9.252%	$34.1413	$34.14	$34.15	$34.10
Purchase #3	$128.36	10.371%	$141.6722	$141.67	$141.65	$141.70
Purchase #4	$170.72	11.801%	$190.8667	$190.87	$190.85	$190.90
Purchase #5	$151.40	13.605%	$171.998	$172.00	$172.00	$172.00
Purchase #6	$116.35	11.822%	$130.1049	$130.10	$130.10	$130.10
Purchase #7	$67.40	8.708%	$73.2692	$73.27	$73.25	$73.30
7 purchase totals =	$791.83		$880.0126	$880.01	$879.95	$880.10