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 $239.97   12.223%   $269.3015   $269.30   $269.30   $269.30  
  Purchase #2 $58.76   11.291%   $65.3946   $65.39   $65.40   $65.40  
  Purchase #3 $118.72   3.378%   $122.7304   $122.73   $122.75   $122.70  
  Purchase #4 $198.76   11.154%   $220.9297   $220.93   $220.95   $220.90  
  Purchase #5 $208.48   5.153%   $219.223   $219.22   $219.20   $219.20  
  Purchase #6 $136.96   5.213%   $144.0997   $144.10   $144.10   $144.10  
  Purchase #7 $10.43   6.401%   $11.0976   $11.10   $11.10   $11.10  
  7 purchase totals = $972.08       $1,052.7765   $1,052.77   $1,052.80   $1,052.70