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 $39.34   5.785%   $41.6158   $41.62   $41.60   $41.60  
  Purchase #2 $203.47   9.775%   $223.3592   $223.36   $223.35   $223.40  
  Purchase #3 $163.74   9.548%   $179.3739   $179.37   $179.35   $179.40  
  Purchase #4 $135.49   4.829%   $142.0328   $142.03   $142.05   $142.00  
  Purchase #5 $53.43   13.361%   $60.5688   $60.57   $60.55   $60.60  
  Purchase #6 $32.50   3.812%   $33.7389   $33.74   $33.75   $33.70  
  Purchase #7 $188.75   3.676%   $195.6885   $195.69   $195.70   $195.70  
  7 purchase totals = $816.72       $876.3779   $876.38   $876.35   $876.40