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 $69.95   12.794%   $78.8994   $78.90   $78.90   $78.90  
  Purchase #2 $157.48   5.399%   $165.9823   $165.98   $166.00   $166.00  
  Purchase #3 $152.48   7.280%   $163.5805   $163.58   $163.60   $163.60  
  Purchase #4 $162.89   8.200%   $176.247   $176.25   $176.25   $176.20  
  Purchase #5 $229.63   13.822%   $261.3695   $261.37   $261.35   $261.40  
  Purchase #6 $196.63   7.348%   $211.0784   $211.08   $211.10   $211.10  
  Purchase #7 $205.26   12.828%   $231.5908   $231.59   $231.60   $231.60  
  7 purchase totals = $1,174.32       $1,288.7479   $1,288.75   $1,288.80   $1,288.80