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 $24.59   8.288%   $26.628   $26.63   $26.65   $26.60  
  Purchase #2 $72.66   5.236%   $76.4645   $76.46   $76.45   $76.50  
  Purchase #3 $195.43   8.519%   $212.0787   $212.08   $212.10   $212.10  
  Purchase #4 $236.96   11.843%   $265.0232   $265.02   $265.00   $265.00  
  Purchase #5 $197.74   12.566%   $222.588   $222.59   $222.60   $222.60  
  Purchase #6 $233.55   5.122%   $245.5124   $245.51   $245.50   $245.50  
  Purchase #7 $249.91   4.470%   $261.081   $261.08   $261.10   $261.10  
  7 purchase totals = $1,210.84       $1,309.3758   $1,309.37   $1,309.40   $1,309.40