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 $119.91   12.464%   $134.8556   $134.86   $134.85   $134.90  
  Purchase #2 $207.54   9.835%   $227.9516   $227.95   $227.95   $228.00  
  Purchase #3 $137.43   6.729%   $146.6777   $146.68   $146.70   $146.70  
  Purchase #4 $95.69   7.238%   $102.616   $102.62   $102.60   $102.60  
  Purchase #5 $241.59   13.250%   $273.6007   $273.60   $273.60   $273.60  
  Purchase #6 $49.59   7.151%   $53.1362   $53.14   $53.15   $53.10  
  Purchase #7 $222.84   6.874%   $238.158   $238.16   $238.15   $238.20  
  7 purchase totals = $1,074.59       $1,176.9958   $1,177.01   $1,177.00   $1,177.10