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 $240.77   4.873%   $252.5027   $252.50   $252.50   $252.50  
  Purchase #2 $196.69   10.322%   $216.9923   $216.99   $217.00   $217.00  
  Purchase #3 $12.25   13.221%   $13.8696   $13.87   $13.85   $13.90  
  Purchase #4 $186.63   9.570%   $204.4905   $204.49   $204.50   $204.50  
  Purchase #5 $246.79   5.782%   $261.0594   $261.06   $261.05   $261.10  
  Purchase #6 $150.56   13.210%   $170.449   $170.45   $170.45   $170.40  
  Purchase #7 $140.66   8.624%   $152.7905   $152.79   $152.80   $152.80  
  7 purchase totals = $1,174.35       $1,272.1540   $1,272.15   $1,272.15   $1,272.20