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 $216.65   5.505%   $228.5766   $228.58   $228.60   $228.60  
  Purchase #2 $146.87   7.127%   $157.3374   $157.34   $157.35   $157.30  
  Purchase #3 $163.59   3.154%   $168.7496   $168.75   $168.75   $168.70  
  Purchase #4 $99.85   7.554%   $107.3927   $107.39   $107.40   $107.40  
  Purchase #5 $78.81   13.629%   $89.551   $89.55   $89.55   $89.60  
  Purchase #6 $72.42   6.145%   $76.8702   $76.87   $76.85   $76.90  
  Purchase #7 $185.54   9.542%   $203.2442   $203.24   $203.25   $203.20  
  7 purchase totals = $963.73       $1,031.7217   $1,031.72   $1,031.75   $1,031.70