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 $92.42   3.599%   $95.7462   $95.75   $95.75   $95.70  
  Purchase #2 $56.53   4.309%   $58.9659   $58.97   $58.95   $59.00  
  Purchase #3 $81.57   4.775%   $85.465   $85.47   $85.45   $85.50  
  Purchase #4 $164.62   7.242%   $176.5418   $176.54   $176.55   $176.50  
  Purchase #5 $52.46   3.116%   $54.0947   $54.09   $54.10   $54.10  
  Purchase #6 $152.93   11.421%   $170.3961   $170.40   $170.40   $170.40  
  Purchase #7 $231.70   3.152%   $239.0032   $239.00   $239.00   $239.00  
  7 purchase totals = $832.23       $880.2129   $880.22   $880.20   $880.20