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	$89.98	12.620%	$101.3355	$101.34	$101.35	$101.30
Purchase #2	$132.89	6.449%	$141.4601	$141.46	$141.45	$141.50
Purchase #3	$90.95	12.215%	$102.0595	$102.06	$102.05	$102.10
Purchase #4	$201.54	10.575%	$222.8529	$222.85	$222.85	$222.90
Purchase #5	$117.75	12.867%	$132.9009	$132.90	$132.90	$132.90
Purchase #6	$47.84	7.776%	$51.56	$51.56	$51.55	$51.60
Purchase #7	$50.95	10.248%	$56.1714	$56.17	$56.15	$56.20
7 purchase totals =	$731.90		$808.3403	$808.34	$808.30	$808.50