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 $103.98   12.829%   $117.3196   $117.32   $117.30   $117.30  
  Purchase #2 $236.87   10.367%   $261.4263   $261.43   $261.45   $261.40  
  Purchase #3 $222.47   11.413%   $247.8605   $247.86   $247.85   $247.90  
  Purchase #4 $134.84   5.418%   $142.1456   $142.15   $142.15   $142.10  
  Purchase #5 $136.68   11.533%   $152.4433   $152.44   $152.45   $152.40  
  Purchase #6 $209.58   7.661%   $225.6359   $225.64   $225.65   $225.60  
  Purchase #7 $28.45   12.863%   $32.1095   $32.11   $32.10   $32.10  
  7 purchase totals = $1,072.87       $1,178.9407   $1,178.95   $1,178.95   $1,178.80