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 $239.53   11.431%   $266.9107   $266.91   $266.90   $266.90  
  Purchase #2 $243.91   4.782%   $255.5738   $255.57   $255.55   $255.60  
  Purchase #3 $179.45   7.678%   $193.2282   $193.23   $193.25   $193.20  
  Purchase #4 $49.61   4.730%   $51.9566   $51.96   $51.95   $52.00  
  Purchase #5 $57.86   9.859%   $63.5644   $63.56   $63.55   $63.60  
  Purchase #6 $247.66   13.147%   $280.2199   $280.22   $280.20   $280.20  
  Purchase #7 $56.57   3.377%   $58.4804   $58.48   $58.50   $58.50  
  7 purchase totals = $1,074.59       $1,169.9340   $1,169.93   $1,169.90   $1,170.00