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 $208.54   13.321%   $236.3196   $236.32   $236.30   $236.30  
  Purchase #2 $181.80   6.359%   $193.3607   $193.36   $193.35   $193.40  
  Purchase #3 $10.53   7.405%   $11.3097   $11.31   $11.30   $11.30  
  Purchase #4 $213.26   9.554%   $233.6349   $233.63   $233.65   $233.60  
  Purchase #5 $235.48   9.604%   $258.0955   $258.10   $258.10   $258.10  
  Purchase #6 $157.78   7.568%   $169.7208   $169.72   $169.70   $169.70  
  Purchase #7 $114.53   8.612%   $124.3933   $124.39   $124.40   $124.40  
  7 purchase totals = $1,121.92       $1,226.8345   $1,226.83   $1,226.80   $1,226.80