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 $91.81   7.646%   $98.8298   $98.83   $98.85   $98.80  
  Purchase #2 $116.25   5.748%   $122.9321   $122.93   $122.95   $122.90  
  Purchase #3 $92.45   13.206%   $104.6589   $104.66   $104.65   $104.70  
  Purchase #4 $101.75   10.532%   $112.4663   $112.47   $112.45   $112.50  
  Purchase #5 $220.62   5.656%   $233.0983   $233.10   $233.10   $233.10  
  Purchase #6 $179.72   12.127%   $201.5146   $201.51   $201.50   $201.50  
  Purchase #7 $152.54   6.857%   $162.9997   $163.00   $163.00   $163.00  
  7 purchase totals = $955.14       $1,036.4997   $1,036.50   $1,036.50   $1,036.50