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 $67.66   12.553%   $76.1534   $76.15   $76.15   $76.20  
  Purchase #2 $192.62   10.540%   $212.9221   $212.92   $212.90   $212.90  
  Purchase #3 $219.59   12.231%   $246.4481   $246.45   $246.45   $246.40  
  Purchase #4 $205.67   10.277%   $226.8067   $226.81   $226.80   $226.80  
  Purchase #5 $62.75   12.556%   $70.6289   $70.63   $70.65   $70.60  
  Purchase #6 $122.66   12.858%   $138.4316   $138.43   $138.45   $138.40  
  Purchase #7 $49.62   13.510%   $56.3237   $56.32   $56.30   $56.30  
  7 purchase totals = $920.57       $1,027.7145   $1,027.71   $1,027.70   $1,027.60