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 $148.95   11.192%   $165.6205   $165.62   $165.60   $165.60  
  Purchase #2 $171.65   12.329%   $192.8127   $192.81   $192.80   $192.80  
  Purchase #3 $230.63   8.543%   $250.3327   $250.33   $250.35   $250.30  
  Purchase #4 $78.32   7.226%   $83.9794   $83.98   $84.00   $84.00  
  Purchase #5 $149.63   3.517%   $154.8925   $154.89   $154.90   $154.90  
  Purchase #6 $132.67   10.161%   $146.1506   $146.15   $146.15   $146.20  
  Purchase #7 $122.60   8.283%   $132.755   $132.76   $132.75   $132.80  
  7 purchase totals = $1,034.45       $1,126.5434   $1,126.54   $1,126.55   $1,126.60