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 $113.41   4.246%   $118.2254   $118.23   $118.25   $118.20  
  Purchase #2 $137.65   12.358%   $154.6608   $154.66   $154.65   $154.70  
  Purchase #3 $26.95   8.185%   $29.1559   $29.16   $29.15   $29.20  
  Purchase #4 $198.32   4.861%   $207.9603   $207.96   $207.95   $208.00  
  Purchase #5 $84.97   7.866%   $91.6537   $91.65   $91.65   $91.70  
  Purchase #6 $14.73   6.556%   $15.6957   $15.70   $15.70   $15.70  
  Purchase #7 $143.41   11.131%   $159.373   $159.37   $159.35   $159.40  
  7 purchase totals = $719.44       $776.7248   $776.73   $776.70   $776.90