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 $43.70   5.682%   $46.183   $46.18   $46.20   $46.20  
  Purchase #2 $90.97   8.522%   $98.7225   $98.72   $98.70   $98.70  
  Purchase #3 $174.54   9.187%   $190.575   $190.58   $190.60   $190.60  
  Purchase #4 $205.48   6.546%   $218.9307   $218.93   $218.95   $218.90  
  Purchase #5 $130.58   7.242%   $140.0366   $140.04   $140.05   $140.00  
  Purchase #6 $61.51   5.563%   $64.9318   $64.93   $64.95   $64.90  
  Purchase #7 $88.53   10.661%   $97.9682   $97.97   $97.95   $98.00  
  7 purchase totals = $795.31       $857.3478   $857.35   $857.40   $857.30