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 $49.98   3.451%   $51.7048   $51.70   $51.70   $51.70  
  Purchase #2 $76.34   8.282%   $82.6625   $82.66   $82.65   $82.70  
  Purchase #3 $35.51   3.121%   $36.6183   $36.62   $36.60   $36.60  
  Purchase #4 $24.97   3.632%   $25.8769   $25.88   $25.90   $25.90  
  Purchase #5 $236.92   13.234%   $268.274   $268.27   $268.25   $268.30  
  Purchase #6 $232.26   10.140%   $255.8112   $255.81   $255.80   $255.80  
  Purchase #7 $62.39   8.476%   $67.6782   $67.68   $67.70   $67.70  
  7 purchase totals = $718.37       $788.6259   $788.62   $788.60   $788.70