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 $116.99   7.732%   $126.0357   $126.04   $126.05   $126.00  
  Purchase #2 $49.83   13.815%   $56.714   $56.71   $56.70   $56.70  
  Purchase #3 $224.64   10.589%   $248.4271   $248.43   $248.45   $248.40  
  Purchase #4 $116.35   10.313%   $128.3492   $128.35   $128.35   $128.30  
  Purchase #5 $193.88   8.457%   $210.2764   $210.28   $210.30   $210.30  
  Purchase #6 $53.46   12.725%   $60.2628   $60.26   $60.25   $60.30  
  Purchase #7 $6.26   7.588%   $6.735   $6.74   $6.75   $6.70  
  7 purchase totals = $761.41       $836.8002   $836.81   $836.85   $836.70