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 $64.61   8.318%   $69.9843   $69.98   $70.00   $70.00  
  Purchase #2 $203.54   11.514%   $226.9756   $226.98   $227.00   $227.00  
  Purchase #3 $70.76   11.449%   $78.8613   $78.86   $78.85   $78.90  
  Purchase #4 $17.51   13.746%   $19.9169   $19.92   $19.90   $19.90  
  Purchase #5 $97.88   9.768%   $107.4409   $107.44   $107.45   $107.40  
  Purchase #6 $162.54   8.723%   $176.7184   $176.72   $176.70   $176.70  
  Purchase #7 $244.67   13.734%   $278.273   $278.27   $278.25   $278.30  
  7 purchase totals = $861.51       $958.1704   $958.17   $958.15   $958.20