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 $182.42   12.321%   $204.896   $204.90   $204.90   $204.90  
  Purchase #2 $83.68   11.514%   $93.3149   $93.31   $93.30   $93.30  
  Purchase #3 $188.97   4.380%   $197.2469   $197.25   $197.25   $197.20  
  Purchase #4 $58.61   3.277%   $60.5306   $60.53   $60.55   $60.50  
  Purchase #5 $248.95   4.716%   $260.6905   $260.69   $260.70   $260.70  
  Purchase #6 $44.41   5.612%   $46.9023   $46.90   $46.90   $46.90  
  Purchase #7 $138.95   10.841%   $154.0136   $154.01   $154.00   $154.00  
  7 purchase totals = $945.99       $1,017.5948   $1,017.59   $1,017.60   $1,017.50