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	$144.59	3.313%	$149.3803	$149.38	$149.40	$149.40
Purchase #2	$207.64	11.850%	$232.2453	$232.25	$232.25	$232.20
Purchase #3	$138.84	8.643%	$150.8399	$150.84	$150.85	$150.80
Purchase #4	$40.30	6.453%	$42.9006	$42.90	$42.90	$42.90
Purchase #5	$190.25	10.310%	$209.8648	$209.86	$209.85	$209.90
Purchase #6	$24.50	3.836%	$25.4398	$25.44	$25.45	$25.40
Purchase #7	$117.64	4.705%	$123.175	$123.18	$123.20	$123.20
7 purchase totals =	$863.76		$933.8457	$933.85	$933.90	$933.80