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 $63.67   12.596%   $71.6899   $71.69   $71.70   $71.70  
  Purchase #2 $40.86   8.717%   $44.4218   $44.42   $44.40   $44.40  
  Purchase #3 $164.47   7.421%   $176.6753   $176.68   $176.70   $176.70  
  Purchase #4 $250.45   3.143%   $258.3216   $258.32   $258.30   $258.30  
  Purchase #5 $86.28   12.422%   $96.9977   $97.00   $97.00   $97.00  
  Purchase #6 $107.28   4.520%   $112.1291   $112.13   $112.15   $112.10  
  Purchase #7 $246.92   9.861%   $271.2688   $271.27   $271.25   $271.30  
  7 purchase totals = $959.93       $1,031.5042   $1,031.51   $1,031.50   $1,031.50