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 $211.36   13.413%   $239.7097   $239.71   $239.70   $239.70  
  Purchase #2 $54.74   8.110%   $59.1794   $59.18   $59.20   $59.20  
  Purchase #3 $64.63   8.270%   $69.9749   $69.97   $69.95   $70.00  
  Purchase #4 $230.36   8.781%   $250.5879   $250.59   $250.60   $250.60  
  Purchase #5 $203.84   8.371%   $220.9034   $220.90   $220.90   $220.90  
  Purchase #6 $135.82   3.156%   $140.1065   $140.11   $140.10   $140.10  
  Purchase #7 $180.47   3.389%   $186.5861   $186.59   $186.60   $186.60  
  7 purchase totals = $1,081.22       $1,167.0479   $1,167.05   $1,167.05   $1,167.10