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 $60.84   12.141%   $68.2266   $68.23   $68.25   $68.20  
  Purchase #2 $237.33   13.776%   $270.0246   $270.02   $270.00   $270.00  
  Purchase #3 $226.50   12.218%   $254.1738   $254.17   $254.15   $254.20  
  Purchase #4 $158.41   4.597%   $165.6921   $165.69   $165.70   $165.70  
  Purchase #5 $246.72   5.137%   $259.394   $259.39   $259.40   $259.40  
  Purchase #6 $223.84   8.335%   $242.4971   $242.50   $242.50   $242.50  
  Purchase #7 $77.35   9.794%   $84.9257   $84.93   $84.95   $84.90  
  7 purchase totals = $1,230.99       $1,344.9339   $1,344.93   $1,344.95   $1,344.90