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 $63.68   5.832%   $67.3938   $67.39   $67.40   $67.40  
  Purchase #2 $248.50   4.629%   $260.0031   $260.00   $260.00   $260.00  
  Purchase #3 $182.54   4.720%   $191.1559   $191.16   $191.15   $191.20  
  Purchase #4 $198.88   5.670%   $210.1565   $210.16   $210.15   $210.20  
  Purchase #5 $127.36   9.119%   $138.974   $138.97   $138.95   $139.00  
  Purchase #6 $116.58   12.757%   $131.4521   $131.45   $131.45   $131.50  
  Purchase #7 $226.36   9.677%   $248.2649   $248.26   $248.25   $248.30  
  7 purchase totals = $1,163.90       $1,247.4003   $1,247.39   $1,247.35   $1,247.60