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 $248.70   7.350%   $266.9795   $266.98   $267.00   $267.00  
  Purchase #2 $168.52   9.365%   $184.3019   $184.30   $184.30   $184.30  
  Purchase #3 $231.75   12.298%   $260.2506   $260.25   $260.25   $260.30  
  Purchase #4 $205.69   8.161%   $222.4764   $222.48   $222.50   $222.50  
  Purchase #5 $83.81   12.649%   $94.4111   $94.41   $94.40   $94.40  
  Purchase #6 $123.95   10.527%   $136.9982   $137.00   $137.00   $137.00  
  Purchase #7 $238.51   8.134%   $257.9104   $257.91   $257.90   $257.90  
  7 purchase totals = $1,300.93       $1,423.3281   $1,423.33   $1,423.35   $1,423.40