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 $224.26   5.377%   $236.3185   $236.32   $236.30   $236.30  
  Purchase #2 $207.98   11.788%   $232.4967   $232.50   $232.50   $232.50  
  Purchase #3 $68.55   8.419%   $74.3212   $74.32   $74.30   $74.30  
  Purchase #4 $78.31   5.696%   $82.7705   $82.77   $82.75   $82.80  
  Purchase #5 $214.88   11.540%   $239.6772   $239.68   $239.70   $239.70  
  Purchase #6 $151.87   12.862%   $171.4035   $171.40   $171.40   $171.40  
  Purchase #7 $240.43   6.477%   $256.0027   $256.00   $256.00   $256.00  
  7 purchase totals = $1,186.28       $1,292.9903   $1,292.99   $1,292.95   $1,293.00