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 $25.62   3.785%   $26.5897   $26.59   $26.60   $26.60  
  Purchase #2 $120.25   5.239%   $126.5499   $126.55   $126.55   $126.50  
  Purchase #3 $166.92   3.291%   $172.4133   $172.41   $172.40   $172.40  
  Purchase #4 $200.36   10.348%   $221.0933   $221.09   $221.10   $221.10  
  Purchase #5 $213.51   3.378%   $220.7224   $220.72   $220.70   $220.70  
  Purchase #6 $193.50   13.413%   $219.4542   $219.45   $219.45   $219.50  
  Purchase #7 $58.47   5.484%   $61.6765   $61.68   $61.70   $61.70  
  7 purchase totals = $978.63       $1,048.4993   $1,048.49   $1,048.50   $1,048.50