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	$242.31	11.345%	$269.8001	$269.80	$269.80	$269.80
Purchase #2	$18.65	6.504%	$19.863	$19.86	$19.85	$19.90
Purchase #3	$119.74	9.864%	$131.5512	$131.55	$131.55	$131.60
Purchase #4	$176.78	8.520%	$191.8417	$191.84	$191.85	$191.80
Purchase #5	$48.34	5.171%	$50.8397	$50.84	$50.85	$50.80
Purchase #6	$168.27	13.314%	$190.6735	$190.67	$190.65	$190.70
Purchase #7	$36.52	6.854%	$39.0231	$39.02	$39.00	$39.00
7 purchase totals =	$810.61		$893.5923	$893.58	$893.55	$893.60