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 $118.73   5.618%   $125.4003   $125.40   $125.40   $125.40  
  Purchase #2 $53.46   3.488%   $55.3247   $55.32   $55.30   $55.30  
  Purchase #3 $144.70   7.196%   $155.1126   $155.11   $155.10   $155.10  
  Purchase #4 $225.60   5.621%   $238.281   $238.28   $238.30   $238.30  
  Purchase #5 $105.47   6.527%   $112.354   $112.35   $112.35   $112.40  
  Purchase #6 $124.60   13.811%   $141.8085   $141.81   $141.80   $141.80  
  Purchase #7 $69.69   11.482%   $77.6918   $77.69   $77.70   $77.70  
  7 purchase totals = $842.25       $905.9729   $905.96   $905.95   $906.00