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 $23.87   7.809%   $25.734   $25.73   $25.75   $25.70  
  Purchase #2 $246.29   10.768%   $272.8105   $272.81   $272.80   $272.80  
  Purchase #3 $27.68   10.207%   $30.5053   $30.51   $30.50   $30.50  
  Purchase #4 $73.72   4.445%   $76.9969   $77.00   $77.00   $77.00  
  Purchase #5 $99.35   12.426%   $111.6952   $111.70   $111.70   $111.70  
  Purchase #6 $90.44   3.165%   $93.3024   $93.30   $93.30   $93.30  
  Purchase #7 $109.31   5.768%   $115.615   $115.62   $115.60   $115.60  
  7 purchase totals = $670.66       $726.6593   $726.67   $726.65   $726.60