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 $148.66   9.621%   $162.9626   $162.96   $162.95   $163.00  
  Purchase #2 $217.56   13.282%   $246.4563   $246.46   $246.45   $246.50  
  Purchase #3 $210.42   9.644%   $230.7129   $230.71   $230.70   $230.70  
  Purchase #4 $126.63   10.406%   $139.8071   $139.81   $139.80   $139.80  
  Purchase #5 $132.60   3.722%   $137.5354   $137.54   $137.55   $137.50  
  Purchase #6 $94.82   10.798%   $105.0587   $105.06   $105.05   $105.10  
  Purchase #7 $44.86   4.127%   $46.7114   $46.71   $46.70   $46.70  
  7 purchase totals = $975.55       $1,069.2444   $1,069.25   $1,069.20   $1,069.30