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 $219.53   13.225%   $248.5628   $248.56   $248.55   $248.60  
  Purchase #2 $206.69   11.207%   $229.8537   $229.85   $229.85   $229.90  
  Purchase #3 $42.88   7.525%   $46.1067   $46.11   $46.10   $46.10  
  Purchase #4 $47.66   10.814%   $52.814   $52.81   $52.80   $52.80  
  Purchase #5 $32.49   4.629%   $33.994   $33.99   $34.00   $34.00  
  Purchase #6 $76.55   13.526%   $86.9042   $86.90   $86.90   $86.90  
  Purchase #7 $185.89   9.369%   $203.306   $203.31   $203.30   $203.30  
  7 purchase totals = $811.69       $901.5414   $901.53   $901.50   $901.60