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 $59.28   7.259%   $63.5831   $63.58   $63.60   $63.60  
  Purchase #2 $161.47   10.569%   $178.5358   $178.54   $178.55   $178.50  
  Purchase #3 $191.69   6.269%   $203.707   $203.71   $203.70   $203.70  
  Purchase #4 $235.65   10.753%   $260.9894   $260.99   $261.00   $261.00  
  Purchase #5 $214.95   4.268%   $224.1241   $224.12   $224.10   $224.10  
  Purchase #6 $84.81   6.146%   $90.0224   $90.02   $90.00   $90.00  
  Purchase #7 $196.74   6.730%   $209.9806   $209.98   $210.00   $210.00  
  7 purchase totals = $1,144.59       $1,230.9424   $1,230.94   $1,230.95   $1,230.90