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 $53.63   10.193%   $59.0965   $59.10   $59.10   $59.10  
  Purchase #2 $63.77   4.762%   $66.8067   $66.81   $66.80   $66.80  
  Purchase #3 $109.41   3.152%   $112.8586   $112.86   $112.85   $112.90  
  Purchase #4 $67.80   11.584%   $75.654   $75.65   $75.65   $75.70  
  Purchase #5 $167.69   7.284%   $179.9045   $179.90   $179.90   $179.90  
  Purchase #6 $113.25   9.628%   $124.1537   $124.15   $124.15   $124.20  
  Purchase #7 $146.63   3.410%   $151.6301   $151.63   $151.65   $151.60  
  7 purchase totals = $722.18       $770.1041   $770.10   $770.10   $770.20