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 $161.57   12.822%   $182.2865   $182.29   $182.30   $182.30  
  Purchase #2 $62.32   8.433%   $67.5754   $67.58   $67.60   $67.60  
  Purchase #3 $12.79   6.318%   $13.5981   $13.60   $13.60   $13.60  
  Purchase #4 $242.57   6.682%   $258.7785   $258.78   $258.80   $258.80  
  Purchase #5 $67.37   8.203%   $72.8964   $72.90   $72.90   $72.90  
  Purchase #6 $206.92   8.544%   $224.5992   $224.60   $224.60   $224.60  
  Purchase #7 $240.34   5.169%   $252.7632   $252.76   $252.75   $252.80  
  7 purchase totals = $993.88       $1,072.4973   $1,072.51   $1,072.55   $1,072.60