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 $81.93   6.143%   $86.963   $86.96   $86.95   $87.00  
  Purchase #2 $134.66   6.752%   $143.7522   $143.75   $143.75   $143.80  
  Purchase #3 $93.26   11.632%   $104.108   $104.11   $104.10   $104.10  
  Purchase #4 $16.96   11.791%   $18.9598   $18.96   $18.95   $19.00  
  Purchase #5 $214.98   7.419%   $230.9294   $230.93   $230.95   $230.90  
  Purchase #6 $172.54   10.605%   $190.8379   $190.84   $190.85   $190.80  
  Purchase #7 $215.34   4.773%   $225.6182   $225.62   $225.60   $225.60  
  7 purchase totals = $929.67       $1,001.1685   $1,001.17   $1,001.15   $1,001.20