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	$76.89	3.465%	$79.5542	$79.55	$79.55	$79.60
Purchase #2	$55.55	7.238%	$59.5707	$59.57	$59.55	$59.60
Purchase #3	$194.85	10.502%	$215.3131	$215.31	$215.30	$215.30
Purchase #4	$138.73	3.171%	$143.1291	$143.13	$143.15	$143.10
Purchase #5	$132.89	4.549%	$138.9352	$138.94	$138.95	$138.90
Purchase #6	$180.42	8.219%	$195.2487	$195.25	$195.25	$195.20
Purchase #7	$43.44	5.443%	$45.8044	$45.80	$45.80	$45.80
7 purchase totals =	$822.77		$877.5554	$877.55	$877.55	$877.50