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 $162.95   12.856%   $183.8989   $183.90   $183.90   $183.90  
  Purchase #2 $88.49   6.772%   $94.4825   $94.48   $94.50   $94.50  
  Purchase #3 $217.65   4.361%   $227.1417   $227.14   $227.15   $227.10  
  Purchase #4 $156.32   12.553%   $175.9428   $175.94   $175.95   $175.90  
  Purchase #5 $16.93   6.252%   $17.9885   $17.99   $18.00   $18.00  
  Purchase #6 $59.29   5.223%   $62.3867   $62.39   $62.40   $62.40  
  Purchase #7 $230.71   9.277%   $252.113   $252.11   $252.10   $252.10  
  7 purchase totals = $932.34       $1,013.9541   $1,013.95   $1,014.00   $1,013.90