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 $216.87   10.377%   $239.3746   $239.37   $239.35   $239.40  
  Purchase #2 $214.71   6.157%   $227.9297   $227.93   $227.95   $227.90  
  Purchase #3 $62.77   13.524%   $71.259   $71.26   $71.25   $71.30  
  Purchase #4 $111.51   5.636%   $117.7947   $117.79   $117.80   $117.80  
  Purchase #5 $210.82   7.662%   $226.973   $226.97   $226.95   $227.00  
  Purchase #6 $137.86   13.486%   $156.4518   $156.45   $156.45   $156.50  
  Purchase #7 $118.66   7.343%   $127.3732   $127.37   $127.35   $127.40  
  7 purchase totals = $1,073.20       $1,167.1560   $1,167.14   $1,167.10   $1,167.30