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 $187.34   11.567%   $209.0096   $209.01   $209.00   $209.00  
  Purchase #2 $242.61   13.338%   $274.9693   $274.97   $274.95   $275.00  
  Purchase #3 $125.74   12.641%   $141.6348   $141.63   $141.65   $141.60  
  Purchase #4 $196.69   13.418%   $223.0819   $223.08   $223.10   $223.10  
  Purchase #5 $143.94   7.423%   $154.6247   $154.62   $154.60   $154.60  
  Purchase #6 $199.29   5.380%   $210.0118   $210.01   $210.00   $210.00  
  Purchase #7 $47.64   12.608%   $53.6465   $53.65   $53.65   $53.60  
  7 purchase totals = $1,143.25       $1,266.9786   $1,266.97   $1,266.95   $1,266.90