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 $98.31   9.483%   $107.6327   $107.63   $107.65   $107.60  
  Purchase #2 $217.83   7.764%   $234.7423   $234.74   $234.75   $234.70  
  Purchase #3 $111.78   8.844%   $121.6658   $121.67   $121.65   $121.70  
  Purchase #4 $93.50   3.207%   $96.4985   $96.50   $96.50   $96.50  
  Purchase #5 $177.69   7.183%   $190.4535   $190.45   $190.45   $190.50  
  Purchase #6 $196.46   7.866%   $211.9135   $211.91   $211.90   $211.90  
  Purchase #7 $99.37   5.557%   $104.892   $104.89   $104.90   $104.90  
  7 purchase totals = $994.94       $1,067.7983   $1,067.79   $1,067.80   $1,067.80