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 $156.95   10.769%   $173.8519   $173.85   $173.85   $173.90  
  Purchase #2 $26.41   3.535%   $27.3436   $27.34   $27.35   $27.30  
  Purchase #3 $118.44   3.541%   $122.634   $122.63   $122.65   $122.60  
  Purchase #4 $220.42   4.694%   $230.7665   $230.77   $230.75   $230.80  
  Purchase #5 $20.54   10.331%   $22.662   $22.66   $22.65   $22.70  
  Purchase #6 $102.38   8.633%   $111.2185   $111.22   $111.20   $111.20  
  Purchase #7 $137.54   13.738%   $156.4352   $156.44   $156.45   $156.40  
  7 purchase totals = $782.68       $844.9117   $844.91   $844.90   $844.90