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	$66.78	3.468%	$69.0959	$69.10	$69.10	$69.10
Purchase #2	$240.98	11.864%	$269.5699	$269.57	$269.55	$269.60
Purchase #3	$108.38	12.295%	$121.7053	$121.71	$121.70	$121.70
Purchase #4	$179.97	6.338%	$191.3765	$191.38	$191.40	$191.40
Purchase #5	$42.80	3.576%	$44.3305	$44.33	$44.35	$44.30
Purchase #6	$156.33	10.208%	$172.2882	$172.29	$172.30	$172.30
Purchase #7	$86.41	4.746%	$90.511	$90.51	$90.50	$90.50
7 purchase totals =	$881.65		$958.8773	$958.89	$958.90	$958.90