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 $57.67   7.413%   $61.9451   $61.95   $61.95   $61.90  
  Purchase #2 $150.75   6.147%   $160.0166   $160.02   $160.00   $160.00  
  Purchase #3 $162.99   4.212%   $169.8551   $169.86   $169.85   $169.90  
  Purchase #4 $124.66   9.824%   $136.9066   $136.91   $136.90   $136.90  
  Purchase #5 $16.88   4.848%   $17.6983   $17.70   $17.70   $17.70  
  Purchase #6 $196.47   3.517%   $203.3798   $203.38   $203.40   $203.40  
  Purchase #7 $65.80   5.798%   $69.6151   $69.62   $69.60   $69.60  
  7 purchase totals = $775.22       $819.4166   $819.44   $819.40   $819.40