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 $46.63   7.119%   $49.9496   $49.95   $49.95   $49.90  
  Purchase #2 $215.25   12.369%   $241.8743   $241.87   $241.85   $241.90  
  Purchase #3 $142.78   13.235%   $161.6769   $161.68   $161.70   $161.70  
  Purchase #4 $132.49   5.807%   $140.1837   $140.18   $140.20   $140.20  
  Purchase #5 $239.58   7.641%   $257.8863   $257.89   $257.90   $257.90  
  Purchase #6 $201.33   9.181%   $219.8141   $219.81   $219.80   $219.80  
  Purchase #7 $106.77   4.766%   $111.8587   $111.86   $111.85   $111.90  
  7 purchase totals = $1,084.83       $1,183.2436   $1,183.24   $1,183.25   $1,183.30