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 $190.81   5.837%   $201.9476   $201.95   $201.95   $201.90  
  Purchase #2 $68.64   4.154%   $71.4913   $71.49   $71.50   $71.50  
  Purchase #3 $78.38   8.448%   $85.0015   $85.00   $85.00   $85.00  
  Purchase #4 $5.48   7.581%   $5.8954   $5.90   $5.90   $5.90  
  Purchase #5 $24.25   6.470%   $25.819   $25.82   $25.80   $25.80  
  Purchase #6 $58.30   5.293%   $61.3858   $61.39   $61.40   $61.40  
  Purchase #7 $26.96   11.240%   $29.9903   $29.99   $30.00   $30.00  
  7 purchase totals = $452.82       $481.5309   $481.54   $481.55   $481.50