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 $94.25   13.712%   $107.1736   $107.17   $107.15   $107.20  
  Purchase #2 $240.30   13.651%   $273.1034   $273.10   $273.10   $273.10  
  Purchase #3 $217.65   8.602%   $236.3723   $236.37   $236.35   $236.40  
  Purchase #4 $25.65   13.386%   $29.0835   $29.08   $29.10   $29.10  
  Purchase #5 $157.31   10.312%   $173.5318   $173.53   $173.55   $173.50  
  Purchase #6 $163.39   3.417%   $168.973   $168.97   $168.95   $169.00  
  Purchase #7 $36.99   3.449%   $38.2658   $38.27   $38.25   $38.30  
  7 purchase totals = $935.54       $1,026.5034   $1,026.49   $1,026.45   $1,026.60