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 $65.88   3.607%   $68.2563   $68.26   $68.25   $68.30  
  Purchase #2 $189.99   7.456%   $204.1557   $204.16   $204.15   $204.20  
  Purchase #3 $30.46   10.259%   $33.5849   $33.58   $33.60   $33.60  
  Purchase #4 $165.46   5.156%   $173.9911   $173.99   $174.00   $174.00  
  Purchase #5 $134.74   8.374%   $146.0231   $146.02   $146.00   $146.00  
  Purchase #6 $250.91   5.247%   $264.0752   $264.08   $264.10   $264.10  
  Purchase #7 $24.87   4.548%   $26.0011   $26.00   $26.00   $26.00  
  7 purchase totals = $862.31       $916.0874   $916.09   $916.10   $916.20