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 $66.46   3.258%   $68.6253   $68.63   $68.65   $68.60  
  Purchase #2 $65.94   8.754%   $71.7124   $71.71   $71.70   $71.70  
  Purchase #3 $51.34   12.708%   $57.8643   $57.86   $57.85   $57.90  
  Purchase #4 $196.57   4.828%   $206.0604   $206.06   $206.05   $206.10  
  Purchase #5 $164.83   7.311%   $176.8807   $176.88   $176.90   $176.90  
  Purchase #6 $184.32   11.446%   $205.4173   $205.42   $205.40   $205.40  
  Purchase #7 $158.72   9.577%   $173.9206   $173.92   $173.90   $173.90  
  7 purchase totals = $888.18       $960.4810   $960.48   $960.45   $960.50