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 $223.76   13.490%   $253.9452   $253.95   $253.95   $253.90  
  Purchase #2 $94.57   12.860%   $106.7317   $106.73   $106.75   $106.70  
  Purchase #3 $166.81   10.289%   $183.9731   $183.97   $183.95   $184.00  
  Purchase #4 $220.81   5.614%   $233.2063   $233.21   $233.20   $233.20  
  Purchase #5 $213.34   6.389%   $226.9703   $226.97   $226.95   $227.00  
  Purchase #6 $200.87   11.536%   $224.0424   $224.04   $224.05   $224.00  
  Purchase #7 $7.71   4.546%   $8.0605   $8.06   $8.05   $8.10  
  7 purchase totals = $1,127.87       $1,236.9295   $1,236.93   $1,236.90   $1,236.90