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 $64.49   3.126%   $66.506   $66.51   $66.50   $66.50  
  Purchase #2 $58.55   11.692%   $65.3957   $65.40   $65.40   $65.40  
  Purchase #3 $94.87   4.153%   $98.81   $98.81   $98.80   $98.80  
  Purchase #4 $197.64   12.398%   $222.1434   $222.14   $222.15   $222.10  
  Purchase #5 $75.77   9.699%   $83.1189   $83.12   $83.10   $83.10  
  Purchase #6 $190.50   8.359%   $206.4239   $206.42   $206.40   $206.40  
  Purchase #7 $217.99   12.270%   $244.7374   $244.74   $244.75   $244.70  
  7 purchase totals = $899.81       $987.1353   $987.14   $987.10   $987.00