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 $144.88   12.491%   $162.977   $162.98   $163.00   $163.00  
  Purchase #2 $86.81   13.829%   $98.815   $98.82   $98.80   $98.80  
  Purchase #3 $123.46   12.238%   $138.569   $138.57   $138.55   $138.60  
  Purchase #4 $239.27   9.466%   $261.9193   $261.92   $261.90   $261.90  
  Purchase #5 $135.47   6.316%   $144.0263   $144.03   $144.05   $144.00  
  Purchase #6 $213.58   6.172%   $226.7622   $226.76   $226.75   $226.80  
  Purchase #7 $166.41   8.744%   $180.9609   $180.96   $180.95   $181.00  
  7 purchase totals = $1,109.88       $1,214.0297   $1,214.04   $1,214.00   $1,214.10