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 $55.69   7.650%   $59.9503   $59.95   $59.95   $60.00  
  Purchase #2 $126.26   13.835%   $143.7281   $143.73   $143.75   $143.70  
  Purchase #3 $184.99   8.743%   $201.1637   $201.16   $201.15   $201.20  
  Purchase #4 $10.85   6.754%   $11.5828   $11.58   $11.60   $11.60  
  Purchase #5 $196.41   9.313%   $214.7017   $214.70   $214.70   $214.70  
  Purchase #6 $54.56   3.787%   $56.6262   $56.63   $56.65   $56.60  
  Purchase #7 $231.31   7.655%   $249.0168   $249.02   $249.00   $249.00  
  7 purchase totals = $860.07       $936.7696   $936.77   $936.80   $936.80