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 $112.36   5.246%   $118.2544   $118.25   $118.25   $118.30  
  Purchase #2 $106.52   13.735%   $121.1505   $121.15   $121.15   $121.20  
  Purchase #3 $70.46   13.855%   $80.2222   $80.22   $80.20   $80.20  
  Purchase #4 $160.54   13.824%   $182.733   $182.73   $182.75   $182.70  
  Purchase #5 $114.92   7.357%   $123.3747   $123.37   $123.35   $123.40  
  Purchase #6 $68.59   7.635%   $73.8268   $73.83   $73.85   $73.80  
  Purchase #7 $61.61   3.361%   $63.6807   $63.68   $63.70   $63.70  
  7 purchase totals = $695.00       $763.2423   $763.23   $763.25   $763.30