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 $248.91   7.468%   $267.4986   $267.50   $267.50   $267.50  
  Purchase #2 $239.36   11.272%   $266.3407   $266.34   $266.35   $266.30  
  Purchase #3 $101.84   12.786%   $114.8613   $114.86   $114.85   $114.90  
  Purchase #4 $171.31   7.692%   $184.4872   $184.49   $184.50   $184.50  
  Purchase #5 $180.32   7.283%   $193.4527   $193.45   $193.45   $193.50  
  Purchase #6 $209.48   4.821%   $219.579   $219.58   $219.60   $219.60  
  Purchase #7 $221.97   7.866%   $239.4302   $239.43   $239.45   $239.40  
  7 purchase totals = $1,373.19       $1,485.6497   $1,485.65   $1,485.70   $1,485.70