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	$11.94	7.432%	$12.8274	$12.83	$12.85	$12.80
Purchase #2	$199.36	8.517%	$216.3395	$216.34	$216.35	$216.30
Purchase #3	$11.70	7.662%	$12.5965	$12.60	$12.60	$12.60
Purchase #4	$152.38	10.364%	$168.1727	$168.17	$168.15	$168.20
Purchase #5	$232.60	3.584%	$240.9364	$240.94	$240.95	$240.90
Purchase #6	$159.74	12.369%	$179.4982	$179.50	$179.50	$179.50
Purchase #7	$12.87	4.738%	$13.4798	$13.48	$13.50	$13.50
7 purchase totals =	$780.59		$843.8505	$843.86	$843.90	$843.80