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 $248.89   4.661%   $260.4908   $260.49   $260.50   $260.50  
  Purchase #2 $119.37   3.263%   $123.265   $123.27   $123.25   $123.30  
  Purchase #3 $49.68   6.657%   $52.9872   $52.99   $53.00   $53.00  
  Purchase #4 $235.65   6.332%   $250.5714   $250.57   $250.55   $250.60  
  Purchase #5 $240.70   10.549%   $266.0914   $266.09   $266.10   $266.10  
  Purchase #6 $200.91   12.120%   $225.2603   $225.26   $225.25   $225.30  
  Purchase #7 $130.97   8.857%   $142.57   $142.57   $142.55   $142.60  
  7 purchase totals = $1,226.17       $1,321.2361   $1,321.24   $1,321.20   $1,321.40