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 $24.66   7.154%   $26.4242   $26.42   $26.40   $26.40  
  Purchase #2 $100.53   3.406%   $103.9541   $103.95   $103.95   $104.00  
  Purchase #3 $163.77   4.128%   $170.5304   $170.53   $170.55   $170.50  
  Purchase #4 $227.26   3.572%   $235.3777   $235.38   $235.40   $235.40  
  Purchase #5 $248.89   7.178%   $266.7553   $266.76   $266.75   $266.80  
  Purchase #6 $116.73   6.750%   $124.6093   $124.61   $124.60   $124.60  
  Purchase #7 $29.78   10.834%   $33.0064   $33.01   $33.00   $33.00  
  7 purchase totals = $911.62       $960.6574   $960.66   $960.65   $960.70