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 $161.26   11.544%   $179.8759   $179.88   $179.90   $179.90  
  Purchase #2 $89.75   9.256%   $98.0573   $98.06   $98.05   $98.10  
  Purchase #3 $62.60   11.869%   $70.03   $70.03   $70.05   $70.00  
  Purchase #4 $60.50   8.428%   $65.5989   $65.60   $65.60   $65.60  
  Purchase #5 $72.91   3.747%   $75.6419   $75.64   $75.65   $75.60  
  Purchase #6 $198.65   9.732%   $217.9826   $217.98   $218.00   $218.00  
  Purchase #7 $112.37   5.874%   $118.9706   $118.97   $118.95   $119.00  
  7 purchase totals = $758.04       $826.1572   $826.16   $826.20   $826.20