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 $118.29   13.613%   $134.3928   $134.39   $134.40   $134.40  
  Purchase #2 $241.57   8.460%   $262.0068   $262.01   $262.00   $262.00  
  Purchase #3 $46.43   3.461%   $48.0369   $48.04   $48.05   $48.00  
  Purchase #4 $40.76   8.783%   $44.34   $44.34   $44.35   $44.30  
  Purchase #5 $158.51   5.552%   $167.3105   $167.31   $167.30   $167.30  
  Purchase #6 $235.26   11.481%   $262.2702   $262.27   $262.25   $262.30  
  Purchase #7 $218.99   3.498%   $226.6503   $226.65   $226.65   $226.70  
  7 purchase totals = $1,059.81       $1,145.0075   $1,145.01   $1,145.00   $1,145.00