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 $235.55   11.513%   $262.6689   $262.67   $262.65   $262.70  
  Purchase #2 $230.41   12.430%   $259.05   $259.05   $259.05   $259.10  
  Purchase #3 $138.61   9.381%   $151.613   $151.61   $151.60   $151.60  
  Purchase #4 $63.98   10.681%   $70.8137   $70.81   $70.80   $70.80  
  Purchase #5 $218.87   9.417%   $239.481   $239.48   $239.50   $239.50  
  Purchase #6 $156.27   6.741%   $166.8042   $166.80   $166.80   $166.80  
  Purchase #7 $100.35   5.741%   $106.1111   $106.11   $106.10   $106.10  
  7 purchase totals = $1,144.04       $1,256.5419   $1,256.53   $1,256.50   $1,256.60