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 $56.40   8.241%   $61.0479   $61.05   $61.05   $61.00  
  Purchase #2 $239.53   6.420%   $254.9078   $254.91   $254.90   $254.90  
  Purchase #3 $214.64   6.109%   $227.7524   $227.75   $227.75   $227.80  
  Purchase #4 $92.65   11.582%   $103.3807   $103.38   $103.40   $103.40  
  Purchase #5 $41.66   13.849%   $47.4295   $47.43   $47.45   $47.40  
  Purchase #6 $187.57   8.611%   $203.7217   $203.72   $203.70   $203.70  
  Purchase #7 $24.89   5.748%   $26.3207   $26.32   $26.30   $26.30  
  7 purchase totals = $857.34       $924.5607   $924.56   $924.55   $924.50