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 $67.42   8.317%   $73.0273   $73.03   $73.05   $73.00  
  Purchase #2 $81.99   9.803%   $90.0275   $90.03   $90.05   $90.00  
  Purchase #3 $86.61   12.824%   $97.7169   $97.72   $97.70   $97.70  
  Purchase #4 $211.83   3.246%   $218.706   $218.71   $218.70   $218.70  
  Purchase #5 $69.41   12.823%   $78.3104   $78.31   $78.30   $78.30  
  Purchase #6 $214.84   12.429%   $241.5425   $241.54   $241.55   $241.50  
  Purchase #7 $28.39   3.332%   $29.336   $29.34   $29.35   $29.30  
  7 purchase totals = $760.49       $828.6666   $828.68   $828.70   $828.50