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	$128.32	9.836%	$140.9416	$140.94	$140.95	$140.90
Purchase #2	$201.78	12.126%	$226.2478	$226.25	$226.25	$226.20
Purchase #3	$87.99	8.365%	$95.3504	$95.35	$95.35	$95.40
Purchase #4	$216.33	10.451%	$238.9386	$238.94	$238.95	$238.90
Purchase #5	$103.91	4.617%	$108.7075	$108.71	$108.70	$108.70
Purchase #6	$157.56	8.871%	$171.5371	$171.54	$171.55	$171.50
Purchase #7	$91.64	9.294%	$100.157	$100.16	$100.15	$100.20
7 purchase totals =	$987.53		$1,081.8800	$1,081.89	$1,081.90	$1,081.80