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 $249.77   4.670%   $261.4343   $261.43   $261.45   $261.40  
  Purchase #2 $146.97   6.824%   $156.9992   $157.00   $157.00   $157.00  
  Purchase #3 $90.32   6.697%   $96.3687   $96.37   $96.35   $96.40  
  Purchase #4 $245.48   9.818%   $269.5812   $269.58   $269.60   $269.60  
  Purchase #5 $101.75   8.418%   $110.3153   $110.32   $110.30   $110.30  
  Purchase #6 $89.67   7.122%   $96.0563   $96.06   $96.05   $96.10  
  Purchase #7 $114.47   4.186%   $119.2617   $119.26   $119.25   $119.30  
  7 purchase totals = $1,038.43       $1,110.0167   $1,110.02   $1,110.00   $1,110.10