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 $24.96   3.704%   $25.8845   $25.88   $25.90   $25.90  
  Purchase #2 $249.71   12.570%   $281.0985   $281.10   $281.10   $281.10  
  Purchase #3 $94.26   13.404%   $106.8946   $106.89   $106.90   $106.90  
  Purchase #4 $133.35   8.129%   $144.19   $144.19   $144.20   $144.20  
  Purchase #5 $248.89   7.168%   $266.7304   $266.73   $266.75   $266.70  
  Purchase #6 $84.94   9.377%   $92.9048   $92.90   $92.90   $92.90  
  Purchase #7 $109.66   13.485%   $124.4477   $124.45   $124.45   $124.40  
  7 purchase totals = $945.77       $1,042.1505   $1,042.14   $1,042.20   $1,042.10