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 $61.90   9.169%   $67.5756   $67.58   $67.60   $67.60  
  Purchase #2 $238.71   3.797%   $247.7738   $247.77   $247.75   $247.80  
  Purchase #3 $23.26   12.652%   $26.2029   $26.20   $26.20   $26.20  
  Purchase #4 $121.94   4.432%   $127.3444   $127.34   $127.35   $127.30  
  Purchase #5 $154.32   6.152%   $163.8138   $163.81   $163.80   $163.80  
  Purchase #6 $145.64   9.396%   $159.3243   $159.32   $159.30   $159.30  
  Purchase #7 $114.28   3.836%   $118.6638   $118.66   $118.65   $118.70  
  7 purchase totals = $860.05       $910.6986   $910.68   $910.65   $910.70