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 $229.58   8.439%   $248.9543   $248.95   $248.95   $249.00  
  Purchase #2 $78.69   12.763%   $88.7332   $88.73   $88.75   $88.70  
  Purchase #3 $6.54   5.156%   $6.8772   $6.88   $6.90   $6.90  
  Purchase #4 $59.97   8.518%   $65.0782   $65.08   $65.10   $65.10  
  Purchase #5 $236.97   11.667%   $264.6173   $264.62   $264.60   $264.60  
  Purchase #6 $208.48   7.802%   $224.7456   $224.75   $224.75   $224.70  
  Purchase #7 $153.26   8.318%   $166.0082   $166.01   $166.00   $166.00  
  7 purchase totals = $973.49       $1,065.0140   $1,065.02   $1,065.05   $1,065.00