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	$80.42	3.131%	$82.938	$82.94	$82.95	$82.90
Purchase #2	$97.80	11.167%	$108.7213	$108.72	$108.70	$108.70
Purchase #3	$130.45	4.159%	$135.8754	$135.88	$135.90	$135.90
Purchase #4	$37.93	13.752%	$43.1461	$43.15	$43.15	$43.10
Purchase #5	$68.80	11.598%	$76.7794	$76.78	$76.80	$76.80
Purchase #6	$104.80	7.722%	$112.8927	$112.89	$112.90	$112.90
Purchase #7	$76.48	7.854%	$82.4867	$82.49	$82.50	$82.50
7 purchase totals =	$596.68		$642.8396	$642.85	$642.90	$642.80