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 $249.87   7.420%   $268.4104   $268.41   $268.40   $268.40  
  Purchase #2 $154.78   13.709%   $175.9988   $176.00   $176.00   $176.00  
  Purchase #3 $25.64   6.869%   $27.4012   $27.40   $27.40   $27.40  
  Purchase #4 $124.95   3.851%   $129.7618   $129.76   $129.75   $129.80  
  Purchase #5 $175.96   8.692%   $191.2544   $191.25   $191.25   $191.30  
  Purchase #6 $137.58   4.638%   $143.961   $143.96   $143.95   $144.00  
  Purchase #7 $55.77   9.853%   $61.265   $61.27   $61.25   $61.30  
  7 purchase totals = $924.55       $998.0526   $998.05   $998.00   $998.20