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	$60.36	10.694%	$66.8149	$66.81	$66.80	$66.80
Purchase #2	$23.46	4.107%	$24.4235	$24.42	$24.40	$24.40
Purchase #3	$246.50	12.105%	$276.3388	$276.34	$276.35	$276.30
Purchase #4	$168.46	10.124%	$185.5149	$185.51	$185.50	$185.50
Purchase #5	$28.27	6.602%	$30.1364	$30.14	$30.15	$30.10
Purchase #6	$183.54	9.431%	$200.8497	$200.85	$200.85	$200.80
Purchase #7	$85.25	6.564%	$90.8458	$90.85	$90.85	$90.80
7 purchase totals =	$795.84		$874.9240	$874.92	$874.90	$874.70