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 $246.45   12.256%   $276.6549   $276.65   $276.65   $276.70  
  Purchase #2 $144.34   13.752%   $164.1896   $164.19   $164.20   $164.20  
  Purchase #3 $9.70   7.490%   $10.4265   $10.43   $10.45   $10.40  
  Purchase #4 $117.94   7.569%   $126.8669   $126.87   $126.85   $126.90  
  Purchase #5 $64.53   13.450%   $73.2093   $73.21   $73.20   $73.20  
  Purchase #6 $39.79   5.558%   $42.0015   $42.00   $42.00   $42.00  
  Purchase #7 $231.63   11.821%   $259.011   $259.01   $259.00   $259.00  
  7 purchase totals = $854.38       $952.3597   $952.36   $952.35   $952.40