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 $81.32   13.441%   $92.2502   $92.25   $92.25   $92.30  
  Purchase #2 $58.27   13.316%   $66.0292   $66.03   $66.05   $66.00  
  Purchase #3 $31.95   12.659%   $35.9946   $35.99   $36.00   $36.00  
  Purchase #4 $150.27   10.791%   $166.4856   $166.49   $166.50   $166.50  
  Purchase #5 $239.93   9.132%   $261.8404   $261.84   $261.85   $261.80  
  Purchase #6 $141.82   9.229%   $154.9086   $154.91   $154.90   $154.90  
  Purchase #7 $179.30   7.858%   $193.3894   $193.39   $193.40   $193.40  
  7 purchase totals = $882.86       $970.8980   $970.90   $970.95   $970.90