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 $61.37   3.676%   $63.626   $63.63   $63.65   $63.60  
  Purchase #2 $110.39   11.615%   $123.2118   $123.21   $123.20   $123.20  
  Purchase #3 $203.80   5.281%   $214.5627   $214.56   $214.55   $214.60  
  Purchase #4 $63.41   4.125%   $66.0257   $66.03   $66.05   $66.00  
  Purchase #5 $166.49   11.674%   $185.926   $185.93   $185.95   $185.90  
  Purchase #6 $92.55   11.151%   $102.8703   $102.87   $102.85   $102.90  
  Purchase #7 $199.66   13.462%   $226.5382   $226.54   $226.55   $226.50  
  7 purchase totals = $897.67       $982.7607   $982.77   $982.80   $982.70