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 $56.92   8.682%   $61.8618   $61.86   $61.85   $61.90  
  Purchase #2 $229.95   7.687%   $247.6263   $247.63   $247.65   $247.60  
  Purchase #3 $236.63   10.451%   $261.3602   $261.36   $261.35   $261.40  
  Purchase #4 $128.59   4.210%   $134.0036   $134.00   $134.00   $134.00  
  Purchase #5 $34.56   10.206%   $38.0872   $38.09   $38.10   $38.10  
  Purchase #6 $138.26   4.646%   $144.6836   $144.68   $144.70   $144.70  
  Purchase #7 $66.38   3.637%   $68.7942   $68.79   $68.80   $68.80  
  7 purchase totals = $891.29       $956.4169   $956.41   $956.45   $956.50