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	$228.85	12.635%	$257.7652	$257.77	$257.75	$257.80
Purchase #2	$111.57	4.666%	$116.7759	$116.78	$116.80	$116.80
Purchase #3	$123.57	11.242%	$137.4617	$137.46	$137.45	$137.50
Purchase #4	$187.94	6.115%	$199.4325	$199.43	$199.45	$199.40
Purchase #5	$128.42	10.486%	$141.8861	$141.89	$141.90	$141.90
Purchase #6	$78.58	10.658%	$86.9551	$86.96	$86.95	$87.00
Purchase #7	$187.51	13.660%	$213.1239	$213.12	$213.10	$213.10
7 purchase totals =	$1,046.44		$1,153.4004	$1,153.41	$1,153.40	$1,153.50