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 $175.73   11.246%   $195.4926   $195.49   $195.50   $195.50  
  Purchase #2 $114.93   8.621%   $124.8381   $124.84   $124.85   $124.80  
  Purchase #3 $17.60   8.271%   $19.0557   $19.06   $19.05   $19.10  
  Purchase #4 $155.75   13.616%   $176.9569   $176.96   $176.95   $177.00  
  Purchase #5 $20.70   11.271%   $23.0331   $23.03   $23.05   $23.00  
  Purchase #6 $124.50   10.859%   $138.0195   $138.02   $138.00   $138.00  
  Purchase #7 $196.66   11.195%   $218.6761   $218.68   $218.70   $218.70  
  7 purchase totals = $805.87       $896.0720   $896.08   $896.10   $896.10