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 $239.93   6.823%   $256.3004   $256.30   $256.30   $256.30  
  Purchase #2 $248.25   8.132%   $268.4377   $268.44   $268.45   $268.40  
  Purchase #3 $51.55   9.577%   $56.4869   $56.49   $56.50   $56.50  
  Purchase #4 $248.31   10.787%   $275.0952   $275.10   $275.10   $275.10  
  Purchase #5 $46.25   11.383%   $51.5146   $51.51   $51.50   $51.50  
  Purchase #6 $48.26   10.326%   $53.2433   $53.24   $53.25   $53.20  
  Purchase #7 $188.79   6.549%   $201.1539   $201.15   $201.15   $201.20  
  7 purchase totals = $1,071.34       $1,162.2320   $1,162.23   $1,162.25   $1,162.20