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 $57.87   10.122%   $63.7276   $63.73   $63.75   $63.70  
  Purchase #2 $50.95   13.437%   $57.7962   $57.80   $57.80   $57.80  
  Purchase #3 $122.81   10.375%   $135.5515   $135.55   $135.55   $135.60  
  Purchase #4 $241.92   3.381%   $250.0993   $250.10   $250.10   $250.10  
  Purchase #5 $58.39   5.735%   $61.7387   $61.74   $61.75   $61.70  
  Purchase #6 $135.98   12.243%   $152.628   $152.63   $152.65   $152.60  
  Purchase #7 $40.78   7.805%   $43.9629   $43.96   $43.95   $44.00  
  7 purchase totals = $708.70       $765.5042   $765.51   $765.55   $765.50