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 $240.28   11.543%   $268.0155   $268.02   $268.00   $268.00  
  Purchase #2 $100.77   4.479%   $105.2835   $105.28   $105.30   $105.30  
  Purchase #3 $233.49   6.119%   $247.7773   $247.78   $247.80   $247.80  
  Purchase #4 $246.84   6.594%   $263.1166   $263.12   $263.10   $263.10  
  Purchase #5 $119.82   3.659%   $124.2042   $124.20   $124.20   $124.20  
  Purchase #6 $240.60   3.176%   $248.2415   $248.24   $248.25   $248.20  
  Purchase #7 $77.45   10.298%   $85.4258   $85.43   $85.45   $85.40  
  7 purchase totals = $1,259.25       $1,342.0644   $1,342.07   $1,342.10   $1,342.00