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 $186.76   9.513%   $204.5265   $204.53   $204.55   $204.50  
  Purchase #2 $72.90   6.484%   $77.6268   $77.63   $77.65   $77.60  
  Purchase #3 $231.86   8.338%   $251.1925   $251.19   $251.20   $251.20  
  Purchase #4 $15.31   9.123%   $16.7067   $16.71   $16.70   $16.70  
  Purchase #5 $222.69   3.608%   $230.7247   $230.72   $230.70   $230.70  
  Purchase #6 $23.67   4.365%   $24.7032   $24.70   $24.70   $24.70  
  Purchase #7 $200.46   8.698%   $217.896   $217.90   $217.90   $217.90  
  7 purchase totals = $953.65       $1,023.3764   $1,023.38   $1,023.40   $1,023.30