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 $57.25   8.729%   $62.2474   $62.25   $62.25   $62.20  
  Purchase #2 $139.91   10.176%   $154.1472   $154.15   $154.15   $154.10  
  Purchase #3 $115.71   5.217%   $121.7466   $121.75   $121.75   $121.70  
  Purchase #4 $227.96   8.579%   $247.5167   $247.52   $247.50   $247.50  
  Purchase #5 $200.75   10.395%   $221.618   $221.62   $221.60   $221.60  
  Purchase #6 $247.61   6.489%   $263.6774   $263.68   $263.70   $263.70  
  Purchase #7 $187.33   11.457%   $208.7924   $208.79   $208.80   $208.80  
  7 purchase totals = $1,176.52       $1,279.7457   $1,279.76   $1,279.75   $1,279.60