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 $55.27   12.690%   $62.2838   $62.28   $62.30   $62.30  
  Purchase #2 $170.40   8.540%   $184.9522   $184.95   $184.95   $185.00  
  Purchase #3 $228.70   8.873%   $248.9926   $248.99   $249.00   $249.00  
  Purchase #4 $23.77   9.750%   $26.0876   $26.09   $26.10   $26.10  
  Purchase #5 $142.41   12.836%   $160.6897   $160.69   $160.70   $160.70  
  Purchase #6 $95.33   12.258%   $107.0156   $107.02   $107.00   $107.00  
  Purchase #7 $152.50   9.589%   $167.1232   $167.12   $167.10   $167.10  
  7 purchase totals = $868.38       $957.1447   $957.14   $957.15   $957.20