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 $233.63   9.547%   $255.9347   $255.93   $255.95   $255.90  
  Purchase #2 $136.31   9.813%   $149.6861   $149.69   $149.70   $149.70  
  Purchase #3 $33.57   11.710%   $37.501   $37.50   $37.50   $37.50  
  Purchase #4 $96.77   13.140%   $109.4856   $109.49   $109.50   $109.50  
  Purchase #5 $174.80   6.241%   $185.7093   $185.71   $185.70   $185.70  
  Purchase #6 $193.86   11.417%   $215.993   $215.99   $216.00   $216.00  
  Purchase #7 $63.85   8.412%   $69.2211   $69.22   $69.20   $69.20  
  7 purchase totals = $932.79       $1,023.5308   $1,023.53   $1,023.55   $1,023.50