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 $113.59   5.154%   $119.4444   $119.44   $119.45   $119.40  
  Purchase #2 $24.86   5.815%   $26.3056   $26.31   $26.30   $26.30  
  Purchase #3 $92.90   3.255%   $95.9239   $95.92   $95.90   $95.90  
  Purchase #4 $42.96   10.765%   $47.5846   $47.58   $47.60   $47.60  
  Purchase #5 $139.56   10.149%   $153.7239   $153.72   $153.70   $153.70  
  Purchase #6 $233.54   6.590%   $248.9303   $248.93   $248.95   $248.90  
  Purchase #7 $24.26   4.422%   $25.3328   $25.33   $25.35   $25.30  
  7 purchase totals = $671.67       $717.2455   $717.23   $717.25   $717.10