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 $177.49   13.814%   $202.0085   $202.01   $202.00   $202.00  
  Purchase #2 $218.43   10.557%   $241.4897   $241.49   $241.50   $241.50  
  Purchase #3 $127.40   12.291%   $143.0587   $143.06   $143.05   $143.10  
  Purchase #4 $231.61   13.523%   $262.9306   $262.93   $262.95   $262.90  
  Purchase #5 $216.96   4.285%   $226.2567   $226.26   $226.25   $226.30  
  Purchase #6 $58.34   3.266%   $60.2454   $60.25   $60.25   $60.20  
  Purchase #7 $228.91   6.333%   $243.4069   $243.41   $243.40   $243.40  
  7 purchase totals = $1,259.14       $1,379.3965   $1,379.41   $1,379.40   $1,379.40