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 $99.70   13.335%   $112.995   $113.00   $113.00   $113.00  
  Purchase #2 $25.63   12.541%   $28.8443   $28.84   $28.85   $28.80  
  Purchase #3 $233.93   9.163%   $255.365   $255.37   $255.35   $255.40  
  Purchase #4 $61.59   3.645%   $63.835   $63.84   $63.85   $63.80  
  Purchase #5 $154.93   8.854%   $168.6475   $168.65   $168.65   $168.60  
  Purchase #6 $24.67   7.357%   $26.485   $26.49   $26.50   $26.50  
  Purchase #7 $201.85   12.330%   $226.7381   $226.74   $226.75   $226.70  
  7 purchase totals = $802.30       $882.9099   $882.93   $882.95   $882.80