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	$195.91	5.185%	$206.0679	$206.07	$206.05	$206.10
Purchase #2	$141.96	13.276%	$160.8066	$160.81	$160.80	$160.80
Purchase #3	$147.83	7.475%	$158.8803	$158.88	$158.90	$158.90
Purchase #4	$80.38	12.693%	$90.5826	$90.58	$90.60	$90.60
Purchase #5	$11.75	10.673%	$13.0041	$13.00	$13.00	$13.00
Purchase #6	$50.89	10.333%	$56.1485	$56.15	$56.15	$56.10
Purchase #7	$139.91	10.801%	$155.0217	$155.02	$155.00	$155.00
7 purchase totals =	$768.63		$840.5117	$840.51	$840.50	$840.50