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 $53.30   13.742%   $60.6245   $60.62   $60.60   $60.60  
  Purchase #2 $190.42   8.365%   $206.3486   $206.35   $206.35   $206.30  
  Purchase #3 $121.81   10.635%   $134.7645   $134.76   $134.75   $134.80  
  Purchase #4 $86.90   7.380%   $93.3132   $93.31   $93.30   $93.30  
  Purchase #5 $73.72   6.679%   $78.6438   $78.64   $78.65   $78.60  
  Purchase #6 $131.57   7.819%   $141.8575   $141.86   $141.85   $141.90  
  Purchase #7 $195.57   12.775%   $220.5541   $220.55   $220.55   $220.60  
  7 purchase totals = $853.29       $936.1062   $936.09   $936.05   $936.10