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 $240.87   9.502%   $263.7575   $263.76   $263.75   $263.80  
  Purchase #2 $175.64   12.569%   $197.7162   $197.72   $197.70   $197.70  
  Purchase #3 $81.81   3.706%   $84.8419   $84.84   $84.85   $84.80  
  Purchase #4 $127.55   13.252%   $144.4529   $144.45   $144.45   $144.50  
  Purchase #5 $119.89   10.404%   $132.3634   $132.36   $132.35   $132.40  
  Purchase #6 $242.92   9.681%   $266.4371   $266.44   $266.45   $266.40  
  Purchase #7 $113.33   10.283%   $124.9837   $124.98   $125.00   $125.00  
  7 purchase totals = $1,102.01       $1,214.5527   $1,214.55   $1,214.55   $1,214.60