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 $232.38   12.519%   $261.4717   $261.47   $261.45   $261.50  
  Purchase #2 $63.78   6.469%   $67.9059   $67.91   $67.90   $67.90  
  Purchase #3 $45.74   7.564%   $49.1998   $49.20   $49.20   $49.20  
  Purchase #4 $87.71   6.820%   $93.6918   $93.69   $93.70   $93.70  
  Purchase #5 $167.51   8.790%   $182.2341   $182.23   $182.25   $182.20  
  Purchase #6 $129.90   6.279%   $138.0564   $138.06   $138.05   $138.10  
  Purchase #7 $142.87   5.417%   $150.6093   $150.61   $150.60   $150.60  
  7 purchase totals = $869.89       $943.1690   $943.17   $943.15   $943.20