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 $58.48   5.466%   $61.6765   $61.68   $61.70   $61.70  
  Purchase #2 $44.50   9.537%   $48.744   $48.74   $48.75   $48.70  
  Purchase #3 $127.55   9.168%   $139.2438   $139.24   $139.25   $139.20  
  Purchase #4 $234.71   13.813%   $267.1305   $267.13   $267.15   $267.10  
  Purchase #5 $14.70   5.519%   $15.5113   $15.51   $15.50   $15.50  
  Purchase #6 $119.85   7.612%   $128.973   $128.97   $128.95   $129.00  
  Purchase #7 $33.28   6.140%   $35.3234   $35.32   $35.30   $35.30  
  7 purchase totals = $633.07       $696.6025   $696.59   $696.60   $696.50