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 $73.99   7.783%   $79.7486   $79.75   $79.75   $79.70  
  Purchase #2 $114.93   9.629%   $125.9966   $126.00   $126.00   $126.00  
  Purchase #3 $200.59   3.178%   $206.9648   $206.96   $206.95   $207.00  
  Purchase #4 $99.50   7.351%   $106.8142   $106.81   $106.80   $106.80  
  Purchase #5 $183.72   13.734%   $208.9521   $208.95   $208.95   $209.00  
  Purchase #6 $73.96   9.808%   $81.214   $81.21   $81.20   $81.20  
  Purchase #7 $109.56   6.334%   $116.4995   $116.50   $116.50   $116.50  
  7 purchase totals = $856.25       $926.1898   $926.18   $926.15   $926.20