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 $24.77   8.760%   $26.9399   $26.94   $26.95   $26.90  
  Purchase #2 $170.50   9.596%   $186.8612   $186.86   $186.85   $186.90  
  Purchase #3 $182.30   6.498%   $194.1459   $194.15   $194.15   $194.10  
  Purchase #4 $225.35   7.172%   $241.5121   $241.51   $241.50   $241.50  
  Purchase #5 $60.62   8.767%   $65.9346   $65.93   $65.95   $65.90  
  Purchase #6 $47.25   13.612%   $53.6817   $53.68   $53.70   $53.70  
  Purchase #7 $114.37   9.603%   $125.353   $125.35   $125.35   $125.40  
  7 purchase totals = $825.16       $894.4284   $894.42   $894.45   $894.40