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 $224.35   13.803%   $255.317   $255.32   $255.30   $255.30  
  Purchase #2 $56.55   8.451%   $61.329   $61.33   $61.35   $61.30  
  Purchase #3 $76.32   10.859%   $84.6076   $84.61   $84.60   $84.60  
  Purchase #4 $73.41   7.670%   $79.0405   $79.04   $79.05   $79.00  
  Purchase #5 $84.25   3.643%   $87.3192   $87.32   $87.30   $87.30  
  Purchase #6 $172.30   8.167%   $186.3717   $186.37   $186.35   $186.40  
  Purchase #7 $39.57   11.547%   $44.1391   $44.14   $44.15   $44.10  
  7 purchase totals = $726.75       $798.1241   $798.13   $798.10   $798.00