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 $34.26   6.202%   $36.3848   $36.38   $36.40   $36.40  
  Purchase #2 $41.91   10.713%   $46.3998   $46.40   $46.40   $46.40  
  Purchase #3 $92.48   6.770%   $98.7409   $98.74   $98.75   $98.70  
  Purchase #4 $218.58   6.442%   $232.6609   $232.66   $232.65   $232.70  
  Purchase #5 $173.87   6.843%   $185.7679   $185.77   $185.75   $185.80  
  Purchase #6 $151.46   9.371%   $165.6533   $165.65   $165.65   $165.70  
  Purchase #7 $24.57   13.553%   $27.9   $27.90   $27.90   $27.90  
  7 purchase totals = $737.13       $793.5076   $793.50   $793.50   $793.60