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 $55.47   5.784%   $58.6784   $58.68   $58.70   $58.70  
  Purchase #2 $147.91   8.137%   $159.9454   $159.95   $159.95   $159.90  
  Purchase #3 $157.46   4.615%   $164.7268   $164.73   $164.75   $164.70  
  Purchase #4 $240.33   12.247%   $269.7632   $269.76   $269.75   $269.80  
  Purchase #5 $47.66   11.262%   $53.0275   $53.03   $53.05   $53.00  
  Purchase #6 $243.73   7.356%   $261.6588   $261.66   $261.65   $261.70  
  Purchase #7 $250.97   6.587%   $267.5014   $267.50   $267.50   $267.50  
  7 purchase totals = $1,143.53       $1,235.3015   $1,235.31   $1,235.35   $1,235.30