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 $62.31   10.746%   $69.0058   $69.01   $69.00   $69.00  
  Purchase #2 $12.57   3.497%   $13.0096   $13.01   $13.00   $13.00  
  Purchase #3 $206.88   9.588%   $226.7157   $226.72   $226.70   $226.70  
  Purchase #4 $64.83   8.329%   $70.2297   $70.23   $70.25   $70.20  
  Purchase #5 $215.27   10.382%   $237.6193   $237.62   $237.60   $237.60  
  Purchase #6 $191.27   3.872%   $198.676   $198.68   $198.70   $198.70  
  Purchase #7 $10.70   6.181%   $11.3614   $11.36   $11.35   $11.40  
  7 purchase totals = $763.83       $826.6175   $826.63   $826.60   $826.60