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 $184.71   10.821%   $204.6975   $204.70   $204.70   $204.70  
  Purchase #2 $192.40   4.685%   $201.4139   $201.41   $201.40   $201.40  
  Purchase #3 $154.68   13.390%   $175.3917   $175.39   $175.40   $175.40  
  Purchase #4 $204.78   4.654%   $214.3105   $214.31   $214.30   $214.30  
  Purchase #5 $8.74   11.531%   $9.7478   $9.75   $9.75   $9.70  
  Purchase #6 $29.81   12.697%   $33.595   $33.60   $33.60   $33.60  
  Purchase #7 $51.36   13.617%   $58.3537   $58.35   $58.35   $58.40  
  7 purchase totals = $826.48       $897.5101   $897.51   $897.50   $897.50