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 $234.55   7.865%   $252.9974   $253.00   $253.00   $253.00  
  Purchase #2 $102.93   13.619%   $116.948   $116.95   $116.95   $116.90  
  Purchase #3 $141.42   3.684%   $146.6299   $146.63   $146.65   $146.60  
  Purchase #4 $249.25   13.280%   $282.3504   $282.35   $282.35   $282.40  
  Purchase #5 $113.97   9.694%   $125.0183   $125.02   $125.00   $125.00  
  Purchase #6 $53.46   11.355%   $59.5304   $59.53   $59.55   $59.50  
  Purchase #7 $206.72   9.151%   $225.6369   $225.64   $225.65   $225.60  
  7 purchase totals = $1,102.30       $1,209.1113   $1,209.12   $1,209.15   $1,209.00