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 $164.32   10.770%   $182.0173   $182.02   $182.00   $182.00  
  Purchase #2 $217.64   3.167%   $224.5327   $224.53   $224.55   $224.50  
  Purchase #3 $27.82   10.687%   $30.7931   $30.79   $30.80   $30.80  
  Purchase #4 $196.91   5.616%   $207.9685   $207.97   $207.95   $208.00  
  Purchase #5 $121.26   4.495%   $126.7106   $126.71   $126.70   $126.70  
  Purchase #6 $230.61   11.332%   $256.7427   $256.74   $256.75   $256.70  
  Purchase #7 $176.75   11.869%   $197.7285   $197.73   $197.75   $197.70  
  7 purchase totals = $1,135.31       $1,226.4934   $1,226.49   $1,226.50   $1,226.40