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 $62.26   8.646%   $67.643   $67.64   $67.65   $67.60  
  Purchase #2 $209.26   8.795%   $227.6644   $227.66   $227.65   $227.70  
  Purchase #3 $219.74   12.846%   $247.9678   $247.97   $247.95   $248.00  
  Purchase #4 $161.78   8.806%   $176.0263   $176.03   $176.05   $176.00  
  Purchase #5 $13.81   13.328%   $15.6506   $15.65   $15.65   $15.70  
  Purchase #6 $157.93   6.822%   $168.704   $168.70   $168.70   $168.70  
  Purchase #7 $82.64   7.528%   $88.8611   $88.86   $88.85   $88.90  
  7 purchase totals = $907.42       $992.5172   $992.51   $992.50   $992.60