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 $59.91   12.725%   $67.5335   $67.53   $67.55   $67.50  
  Purchase #2 $164.43   10.426%   $181.5735   $181.57   $181.55   $181.60  
  Purchase #3 $218.31   5.516%   $230.352   $230.35   $230.35   $230.40  
  Purchase #4 $121.43   9.730%   $133.2451   $133.25   $133.25   $133.20  
  Purchase #5 $249.88   9.601%   $273.871   $273.87   $273.85   $273.90  
  Purchase #6 $193.90   7.779%   $208.9835   $208.98   $209.00   $209.00  
  Purchase #7 $21.87   8.177%   $23.6583   $23.66   $23.65   $23.70  
  7 purchase totals = $1,029.73       $1,119.2169   $1,119.21   $1,119.20   $1,119.30