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	$16.35	6.421%	$17.3998	$17.40	$17.40	$17.40
Purchase #2	$174.54	12.554%	$196.4518	$196.45	$196.45	$196.50
Purchase #3	$134.41	7.688%	$144.7434	$144.74	$144.75	$144.70
Purchase #4	$115.76	13.290%	$131.1445	$131.14	$131.15	$131.10
Purchase #5	$120.67	11.824%	$134.938	$134.94	$134.95	$134.90
Purchase #6	$24.98	11.417%	$27.832	$27.83	$27.85	$27.80
Purchase #7	$84.72	6.365%	$90.1124	$90.11	$90.10	$90.10
7 purchase totals =	$671.43		$742.6219	$742.61	$742.65	$742.50