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 $182.53   10.172%   $201.097   $201.10   $201.10   $201.10  
  Purchase #2 $162.63   11.500%   $181.3325   $181.33   $181.35   $181.30  
  Purchase #3 $15.43   13.596%   $17.5279   $17.53   $17.55   $17.50  
  Purchase #4 $45.62   3.826%   $47.3654   $47.37   $47.35   $47.40  
  Purchase #5 $102.89   5.579%   $108.6302   $108.63   $108.65   $108.60  
  Purchase #6 $55.83   5.799%   $59.0676   $59.07   $59.05   $59.10  
  Purchase #7 $190.59   12.304%   $214.0402   $214.04   $214.05   $214.00  
  7 purchase totals = $755.52       $829.0608   $829.07   $829.10   $829.00