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	$131.89	3.781%	$136.8768	$136.88	$136.90	$136.90
Purchase #2	$69.75	12.761%	$78.6508	$78.65	$78.65	$78.70
Purchase #3	$179.26	11.477%	$199.8337	$199.83	$199.85	$199.80
Purchase #4	$78.37	9.554%	$85.8575	$85.86	$85.85	$85.90
Purchase #5	$82.46	9.850%	$90.5823	$90.58	$90.60	$90.60
Purchase #6	$203.93	8.595%	$221.4578	$221.46	$221.45	$221.50
Purchase #7	$101.71	12.846%	$114.7757	$114.78	$114.80	$114.80
7 purchase totals =	$847.37		$928.0346	$928.04	$928.10	$928.20