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 $193.37   8.577%   $209.9553   $209.96   $209.95   $210.00  
  Purchase #2 $173.94   10.226%   $191.7271   $191.73   $191.75   $191.70  
  Purchase #3 $24.51   10.268%   $27.0267   $27.03   $27.05   $27.00  
  Purchase #4 $189.34   6.154%   $200.992   $200.99   $201.00   $201.00  
  Purchase #5 $184.97   13.136%   $209.2677   $209.27   $209.25   $209.30  
  Purchase #6 $73.66   3.706%   $76.3898   $76.39   $76.40   $76.40  
  Purchase #7 $153.88   6.253%   $163.5021   $163.50   $163.50   $163.50  
  7 purchase totals = $993.67       $1,078.8607   $1,078.87   $1,078.90   $1,078.90