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	$31.45	3.511%	$32.5542	$32.55	$32.55	$32.60
Purchase #2	$90.75	10.268%	$100.0682	$100.07	$100.05	$100.10
Purchase #3	$21.98	8.511%	$23.8507	$23.85	$23.85	$23.90
Purchase #4	$73.48	11.627%	$82.0235	$82.02	$82.00	$82.00
Purchase #5	$22.73	12.873%	$25.656	$25.66	$25.65	$25.70
Purchase #6	$109.30	9.292%	$119.4562	$119.46	$119.45	$119.50
Purchase #7	$60.83	4.116%	$63.3338	$63.33	$63.35	$63.30
7 purchase totals =	$410.52		$446.9426	$446.94	$446.90	$447.10