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	$86.45	4.181%	$90.0645	$90.06	$90.05	$90.10
Purchase #2	$124.55	6.645%	$132.8263	$132.83	$132.85	$132.80
Purchase #3	$227.48	10.216%	$250.7194	$250.72	$250.70	$250.70
Purchase #4	$204.77	8.215%	$221.5919	$221.59	$221.60	$221.60
Purchase #5	$50.34	11.217%	$55.9866	$55.99	$56.00	$56.00
Purchase #6	$65.36	8.257%	$70.7568	$70.76	$70.75	$70.80
Purchase #7	$97.35	4.714%	$101.9391	$101.94	$101.95	$101.90
7 purchase totals =	$856.30		$923.8846	$923.89	$923.90	$923.90