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	$117.34	12.274%	$131.7423	$131.74	$131.75	$131.70
Purchase #2	$37.67	4.205%	$39.254	$39.25	$39.25	$39.30
Purchase #3	$45.71	8.148%	$49.4345	$49.43	$49.45	$49.40
Purchase #4	$240.96	3.819%	$250.1623	$250.16	$250.15	$250.20
Purchase #5	$202.72	7.355%	$217.6301	$217.63	$217.65	$217.60
Purchase #6	$85.57	5.797%	$90.5305	$90.53	$90.55	$90.50
Purchase #7	$29.81	11.475%	$33.2307	$33.23	$33.25	$33.20
7 purchase totals =	$759.78		$811.9844	$811.97	$812.05	$811.90