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	$31.50	4.504%	$32.9188	$32.92	$32.90	$32.90
Purchase #2	$212.60	9.584%	$232.9756	$232.98	$233.00	$233.00
Purchase #3	$196.31	6.190%	$208.4616	$208.46	$208.45	$208.50
Purchase #4	$70.35	4.456%	$73.4848	$73.48	$73.50	$73.50
Purchase #5	$186.86	6.344%	$198.7144	$198.71	$198.70	$198.70
Purchase #6	$7.64	3.567%	$7.9125	$7.91	$7.90	$7.90
Purchase #7	$37.45	10.353%	$41.3272	$41.33	$41.35	$41.30
7 purchase totals =	$742.71		$795.7949	$795.79	$795.80	$795.80