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 $63.72   5.287%   $67.0889   $67.09   $67.10   $67.10  
  Purchase #2 $193.74   10.521%   $214.1234   $214.12   $214.10   $214.10  
  Purchase #3 $77.52   4.791%   $81.234   $81.23   $81.25   $81.20  
  Purchase #4 $190.37   12.637%   $214.4271   $214.43   $214.45   $214.40  
  Purchase #5 $92.74   12.198%   $104.0524   $104.05   $104.05   $104.10  
  Purchase #6 $104.87   10.225%   $115.593   $115.59   $115.60   $115.60  
  Purchase #7 $156.34   4.629%   $163.577   $163.58   $163.60   $163.60  
  7 purchase totals = $879.30       $960.0958   $960.09   $960.15   $960.10