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 $28.87   12.834%   $32.5752   $32.58   $32.60   $32.60  
  Purchase #2 $228.90   13.507%   $259.8175   $259.82   $259.80   $259.80  
  Purchase #3 $10.43   7.838%   $11.2475   $11.25   $11.25   $11.20  
  Purchase #4 $186.72   6.792%   $199.402   $199.40   $199.40   $199.40  
  Purchase #5 $241.69   8.280%   $261.7019   $261.70   $261.70   $261.70  
  Purchase #6 $226.80   12.417%   $254.9618   $254.96   $254.95   $255.00  
  Purchase #7 $162.88   12.754%   $183.6537   $183.65   $183.65   $183.70  
  7 purchase totals = $1,086.29       $1,203.3596   $1,203.36   $1,203.35   $1,203.40