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	$69.97	12.208%	$78.5119	$78.51	$78.50	$78.50
Purchase #2	$204.96	6.851%	$219.0018	$219.00	$219.00	$219.00
Purchase #3	$75.70	10.303%	$83.4994	$83.50	$83.50	$83.50
Purchase #4	$22.89	11.472%	$25.5159	$25.52	$25.50	$25.50
Purchase #5	$186.68	6.154%	$198.1683	$198.17	$198.15	$198.20
Purchase #6	$200.59	11.140%	$222.9357	$222.94	$222.95	$222.90
Purchase #7	$117.89	11.168%	$131.056	$131.06	$131.05	$131.10
7 purchase totals =	$878.68		$958.6890	$958.70	$958.65	$958.70