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 $151.80   8.419%   $164.58   $164.58   $164.60   $164.60  
  Purchase #2 $193.45   3.647%   $200.5051   $200.51   $200.50   $200.50  
  Purchase #3 $61.81   3.576%   $64.0203   $64.02   $64.00   $64.00  
  Purchase #4 $169.80   3.870%   $176.3713   $176.37   $176.35   $176.40  
  Purchase #5 $208.60   5.749%   $220.5924   $220.59   $220.60   $220.60  
  Purchase #6 $202.64   4.243%   $211.238   $211.24   $211.25   $211.20  
  Purchase #7 $29.99   5.863%   $31.7483   $31.75   $31.75   $31.70  
  7 purchase totals = $1,018.09       $1,069.0554   $1,069.06   $1,069.05   $1,069.00