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 $156.69   3.200%   $161.7041   $161.70   $161.70   $161.70  
  Purchase #2 $43.97   11.391%   $48.9786   $48.98   $49.00   $49.00  
  Purchase #3 $74.81   6.863%   $79.9442   $79.94   $79.95   $79.90  
  Purchase #4 $246.38   10.512%   $272.2795   $272.28   $272.30   $272.30  
  Purchase #5 $80.65   4.409%   $84.2059   $84.21   $84.20   $84.20  
  Purchase #6 $233.95   11.519%   $260.8987   $260.90   $260.90   $260.90  
  Purchase #7 $50.85   9.375%   $55.6172   $55.62   $55.60   $55.60  
  7 purchase totals = $887.30       $963.6282   $963.63   $963.65   $963.60