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 $233.44   9.489%   $255.5911   $255.59   $255.60   $255.60  
  Purchase #2 $58.89   10.344%   $64.9816   $64.98   $65.00   $65.00  
  Purchase #3 $95.55   8.743%   $103.9039   $103.90   $103.90   $103.90  
  Purchase #4 $29.99   5.667%   $31.6895   $31.69   $31.70   $31.70  
  Purchase #5 $90.96   5.530%   $95.9901   $95.99   $96.00   $96.00  
  Purchase #6 $56.66   9.134%   $61.8353   $61.84   $61.85   $61.80  
  Purchase #7 $106.68   5.821%   $112.8898   $112.89   $112.90   $112.90  
  7 purchase totals = $672.17       $726.8813   $726.88   $726.95   $726.90