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 $216.42   9.602%   $237.2006   $237.20   $237.20   $237.20  
  Purchase #2 $31.58   9.238%   $34.4974   $34.50   $34.50   $34.50  
  Purchase #3 $113.59   5.186%   $119.4808   $119.48   $119.50   $119.50  
  Purchase #4 $168.60   11.632%   $188.2116   $188.21   $188.20   $188.20  
  Purchase #5 $211.95   6.278%   $225.2562   $225.26   $225.25   $225.30  
  Purchase #6 $7.59   9.457%   $8.3078   $8.31   $8.30   $8.30  
  Purchase #7 $248.66   6.815%   $265.6062   $265.61   $265.60   $265.60  
  7 purchase totals = $998.39       $1,078.5606   $1,078.57   $1,078.55   $1,078.60