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 $66.81   13.434%   $75.7853   $75.79   $75.80   $75.80  
  Purchase #2 $57.73   7.255%   $61.9183   $61.92   $61.90   $61.90  
  Purchase #3 $103.90   5.789%   $109.9148   $109.91   $109.90   $109.90  
  Purchase #4 $46.48   4.842%   $48.7306   $48.73   $48.75   $48.70  
  Purchase #5 $11.66   8.361%   $12.6349   $12.63   $12.65   $12.60  
  Purchase #6 $208.95   10.408%   $230.6975   $230.70   $230.70   $230.70  
  Purchase #7 $103.42   10.535%   $114.3153   $114.32   $114.30   $114.30  
  7 purchase totals = $598.95       $653.9967   $654.00   $654.00   $653.90