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 $244.58   4.419%   $255.388   $255.39   $255.40   $255.40  
  Purchase #2 $233.26   3.527%   $241.4871   $241.49   $241.50   $241.50  
  Purchase #3 $215.42   8.730%   $234.2262   $234.23   $234.25   $234.20  
  Purchase #4 $248.41   6.166%   $263.727   $263.73   $263.75   $263.70  
  Purchase #5 $131.28   12.287%   $147.4104   $147.41   $147.40   $147.40  
  Purchase #6 $124.48   11.740%   $139.094   $139.09   $139.10   $139.10  
  Purchase #7 $75.45   13.546%   $85.6705   $85.67   $85.65   $85.70  
  7 purchase totals = $1,272.88       $1,367.0032   $1,367.01   $1,367.05   $1,367.00