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 $248.41   6.773%   $265.2348   $265.23   $265.25   $265.20  
  Purchase #2 $121.86   13.643%   $138.4854   $138.49   $138.50   $138.50  
  Purchase #3 $193.60   4.813%   $202.918   $202.92   $202.90   $202.90  
  Purchase #4 $12.96   5.677%   $13.6957   $13.70   $13.70   $13.70  
  Purchase #5 $53.63   5.103%   $56.3667   $56.37   $56.35   $56.40  
  Purchase #6 $152.58   9.126%   $166.5045   $166.50   $166.50   $166.50  
  Purchase #7 $111.37   5.463%   $117.4541   $117.45   $117.45   $117.50  
  7 purchase totals = $894.41       $960.6592   $960.66   $960.65   $960.70