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	$27.77	13.573%	$31.5392	$31.54	$31.55	$31.50
Purchase #2	$7.82	11.830%	$8.7451	$8.75	$8.75	$8.70
Purchase #3	$38.83	9.437%	$42.4944	$42.49	$42.50	$42.50
Purchase #4	$179.96	8.296%	$194.8895	$194.89	$194.90	$194.90
Purchase #5	$126.81	13.227%	$143.5832	$143.58	$143.60	$143.60
Purchase #6	$93.28	12.134%	$104.5986	$104.60	$104.60	$104.60
Purchase #7	$89.79	5.378%	$94.6189	$94.62	$94.60	$94.60
7 purchase totals =	$564.26		$620.4689	$620.47	$620.50	$620.40