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 $155.27   8.718%   $168.8064   $168.81   $168.80   $168.80  
  Purchase #2 $179.62   12.405%   $201.9019   $201.90   $201.90   $201.90  
  Purchase #3 $57.76   4.758%   $60.5082   $60.51   $60.50   $60.50  
  Purchase #4 $110.79   6.227%   $117.6889   $117.69   $117.70   $117.70  
  Purchase #5 $55.74   13.124%   $63.0553   $63.06   $63.05   $63.10  
  Purchase #6 $108.44   8.282%   $117.421   $117.42   $117.40   $117.40  
  Purchase #7 $28.96   4.669%   $30.3121   $30.31   $30.30   $30.30  
  7 purchase totals = $696.58       $759.6938   $759.70   $759.65   $759.70