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 $148.81   6.665%   $158.7282   $158.73   $158.75   $158.70  
  Purchase #2 $177.47   9.275%   $193.9303   $193.93   $193.95   $193.90  
  Purchase #3 $217.76   4.464%   $227.4808   $227.48   $227.50   $227.50  
  Purchase #4 $67.29   7.341%   $72.2298   $72.23   $72.25   $72.20  
  Purchase #5 $18.76   3.336%   $19.3858   $19.39   $19.40   $19.40  
  Purchase #6 $120.99   8.242%   $130.962   $130.96   $130.95   $131.00  
  Purchase #7 $171.68   6.830%   $183.4057   $183.41   $183.40   $183.40  
  7 purchase totals = $922.76       $986.1226   $986.13   $986.20   $986.10