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 $193.44   6.601%   $206.209   $206.21   $206.20   $206.20  
  Purchase #2 $50.89   4.854%   $53.3602   $53.36   $53.35   $53.40  
  Purchase #3 $5.44   10.221%   $5.996   $6.00   $6.00   $6.00  
  Purchase #4 $57.65   8.289%   $62.4286   $62.43   $62.45   $62.40  
  Purchase #5 $95.87   5.703%   $101.3375   $101.34   $101.35   $101.30  
  Purchase #6 $248.39   12.833%   $280.2659   $280.27   $280.25   $280.30  
  Purchase #7 $158.64   8.204%   $171.6548   $171.65   $171.65   $171.70  
  7 purchase totals = $810.32       $881.2520   $881.26   $881.25   $881.30