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 $181.49   13.467%   $205.9313   $205.93   $205.95   $205.90  
  Purchase #2 $179.28   7.144%   $192.0878   $192.09   $192.10   $192.10  
  Purchase #3 $66.66   11.605%   $74.3959   $74.40   $74.40   $74.40  
  Purchase #4 $140.97   6.854%   $150.6321   $150.63   $150.65   $150.60  
  Purchase #5 $146.90   6.677%   $156.7085   $156.71   $156.70   $156.70  
  Purchase #6 $63.99   7.302%   $68.6625   $68.66   $68.65   $68.70  
  Purchase #7 $164.38   8.139%   $177.7589   $177.76   $177.75   $177.80  
  7 purchase totals = $943.67       $1,026.1770   $1,026.18   $1,026.20   $1,026.20