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 $84.94   13.493%   $96.401   $96.40   $96.40   $96.40  
  Purchase #2 $250.81   5.273%   $264.0352   $264.04   $264.05   $264.00  
  Purchase #3 $87.63   8.122%   $94.7473   $94.75   $94.75   $94.70  
  Purchase #4 $214.35   3.819%   $222.536   $222.54   $222.55   $222.50  
  Purchase #5 $191.54   5.645%   $202.3524   $202.35   $202.35   $202.40  
  Purchase #6 $193.62   13.341%   $219.4508   $219.45   $219.45   $219.50  
  Purchase #7 $127.83   9.546%   $140.0327   $140.03   $140.05   $140.00  
  7 purchase totals = $1,150.72       $1,239.5554   $1,239.56   $1,239.60   $1,239.50