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 $63.69   7.786%   $68.6489   $68.65   $68.65   $68.60  
  Purchase #2 $96.67   11.520%   $107.8064   $107.81   $107.80   $107.80  
  Purchase #3 $86.91   7.641%   $93.5508   $93.55   $93.55   $93.60  
  Purchase #4 $151.60   8.237%   $164.0873   $164.09   $164.10   $164.10  
  Purchase #5 $248.75   7.674%   $267.8391   $267.84   $267.85   $267.80  
  Purchase #6 $244.55   11.778%   $273.3531   $273.35   $273.35   $273.40  
  Purchase #7 $8.85   12.709%   $9.9747   $9.97   $9.95   $10.00  
  7 purchase totals = $901.02       $985.2603   $985.26   $985.25   $985.30