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 $54.54   3.141%   $56.2531   $56.25   $56.25   $56.30  
  Purchase #2 $73.33   13.693%   $83.3711   $83.37   $83.35   $83.40  
  Purchase #3 $104.75   12.334%   $117.6699   $117.67   $117.65   $117.70  
  Purchase #4 $106.85   13.188%   $120.9414   $120.94   $120.95   $120.90  
  Purchase #5 $200.39   3.184%   $206.7704   $206.77   $206.75   $206.80  
  Purchase #6 $228.56   9.652%   $250.6206   $250.62   $250.60   $250.60  
  Purchase #7 $63.33   7.439%   $68.0411   $68.04   $68.05   $68.00  
  7 purchase totals = $831.75       $903.6676   $903.66   $903.60   $903.70