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 $88.89   5.167%   $93.4829   $93.48   $93.50   $93.50  
  Purchase #2 $214.69   11.488%   $239.3536   $239.35   $239.35   $239.40  
  Purchase #3 $140.58   12.479%   $158.123   $158.12   $158.10   $158.10  
  Purchase #4 $67.35   9.228%   $73.5651   $73.57   $73.55   $73.60  
  Purchase #5 $242.93   6.329%   $258.305   $258.31   $258.30   $258.30  
  Purchase #6 $216.69   8.400%   $234.892   $234.89   $234.90   $234.90  
  Purchase #7 $69.41   9.370%   $75.9137   $75.91   $75.90   $75.90  
  7 purchase totals = $1,040.54       $1,133.6353   $1,133.63   $1,133.60   $1,133.70