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 $245.28   7.376%   $263.3719   $263.37   $263.35   $263.40  
  Purchase #2 $47.37   5.391%   $49.9237   $49.92   $49.90   $49.90  
  Purchase #3 $39.54   7.479%   $42.4972   $42.50   $42.50   $42.50  
  Purchase #4 $56.87   10.786%   $63.004   $63.00   $63.00   $63.00  
  Purchase #5 $69.89   13.498%   $79.3238   $79.32   $79.30   $79.30  
  Purchase #6 $11.31   11.133%   $12.5691   $12.57   $12.55   $12.60  
  Purchase #7 $232.97   12.538%   $262.1798   $262.18   $262.20   $262.20  
  7 purchase totals = $703.23       $772.8695   $772.86   $772.80   $772.90