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 $148.93   8.720%   $161.9167   $161.92   $161.90   $161.90  
  Purchase #2 $246.44   8.786%   $268.0922   $268.09   $268.10   $268.10  
  Purchase #3 $85.28   13.373%   $96.6845   $96.68   $96.70   $96.70  
  Purchase #4 $93.67   5.648%   $98.9605   $98.96   $98.95   $99.00  
  Purchase #5 $112.61   13.370%   $127.666   $127.67   $127.65   $127.70  
  Purchase #6 $55.26   7.217%   $59.2481   $59.25   $59.25   $59.20  
  Purchase #7 $80.50   8.621%   $87.4399   $87.44   $87.45   $87.40  
  7 purchase totals = $822.69       $900.0079   $900.01   $900.00   $900.00