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 $228.40   8.644%   $248.1429   $248.14   $248.15   $248.10  
  Purchase #2 $118.98   12.374%   $133.7026   $133.70   $133.70   $133.70  
  Purchase #3 $193.65   11.778%   $216.4581   $216.46   $216.45   $216.50  
  Purchase #4 $222.94   6.418%   $237.2483   $237.25   $237.25   $237.20  
  Purchase #5 $53.56   11.820%   $59.8908   $59.89   $59.90   $59.90  
  Purchase #6 $126.58   12.193%   $142.0139   $142.01   $142.00   $142.00  
  Purchase #7 $240.50   4.436%   $251.1686   $251.17   $251.15   $251.20  
  7 purchase totals = $1,184.61       $1,288.6252   $1,288.62   $1,288.60   $1,288.60