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 $63.88   4.212%   $66.5706   $66.57   $66.55   $66.60  
  Purchase #2 $116.99   7.297%   $125.5268   $125.53   $125.55   $125.50  
  Purchase #3 $60.99   13.116%   $68.9894   $68.99   $69.00   $69.00  
  Purchase #4 $60.31   13.318%   $68.3421   $68.34   $68.35   $68.30  
  Purchase #5 $111.52   10.223%   $122.9207   $122.92   $122.90   $122.90  
  Purchase #6 $214.61   7.168%   $229.9932   $229.99   $230.00   $230.00  
  Purchase #7 $26.40   7.365%   $28.3444   $28.34   $28.35   $28.30  
  7 purchase totals = $654.70       $710.6872   $710.68   $710.70   $710.60