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 $57.39   12.868%   $64.7749   $64.77   $64.75   $64.80  
  Purchase #2 $165.29   9.522%   $181.0289   $181.03   $181.05   $181.00  
  Purchase #3 $168.48   5.581%   $177.8829   $177.88   $177.90   $177.90  
  Purchase #4 $104.69   5.609%   $110.5621   $110.56   $110.55   $110.60  
  Purchase #5 $114.77   8.604%   $124.6448   $124.64   $124.65   $124.60  
  Purchase #6 $58.85   11.218%   $65.4518   $65.45   $65.45   $65.50  
  Purchase #7 $208.76   12.867%   $235.6211   $235.62   $235.60   $235.60  
  7 purchase totals = $878.23       $959.9665   $959.95   $959.95   $960.00