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	$205.99	7.798%	$222.0531	$222.05	$222.05	$222.10
Purchase #2	$36.46	5.184%	$38.3501	$38.35	$38.35	$38.40
Purchase #3	$187.37	12.532%	$210.8512	$210.85	$210.85	$210.90
Purchase #4	$206.44	7.783%	$222.5072	$222.51	$222.50	$222.50
Purchase #5	$82.99	9.477%	$90.855	$90.86	$90.85	$90.90
Purchase #6	$18.58	12.836%	$20.9649	$20.96	$20.95	$21.00
Purchase #7	$124.70	12.817%	$140.6828	$140.68	$140.70	$140.70
7 purchase totals =	$862.53		$946.2643	$946.26	$946.25	$946.50