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 $193.93   10.469%   $214.2325   $214.23   $214.25   $214.20  
  Purchase #2 $96.93   6.649%   $103.3749   $103.37   $103.35   $103.40  
  Purchase #3 $250.39   3.728%   $259.7245   $259.72   $259.70   $259.70  
  Purchase #4 $194.46   12.457%   $218.6839   $218.68   $218.70   $218.70  
  Purchase #5 $179.48   9.782%   $197.0367   $197.04   $197.05   $197.00  
  Purchase #6 $135.62   4.506%   $141.731   $141.73   $141.75   $141.70  
  Purchase #7 $12.62   7.786%   $13.6026   $13.60   $13.60   $13.60  
  7 purchase totals = $1,063.43       $1,148.3861   $1,148.37   $1,148.40   $1,148.30