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 $56.44   10.215%   $62.2053   $62.21   $62.20   $62.20  
  Purchase #2 $98.92   4.873%   $103.7404   $103.74   $103.75   $103.70  
  Purchase #3 $63.68   6.653%   $67.9166   $67.92   $67.90   $67.90  
  Purchase #4 $211.29   12.249%   $237.1709   $237.17   $237.15   $237.20  
  Purchase #5 $6.69   8.264%   $7.2429   $7.24   $7.25   $7.20  
  Purchase #6 $76.94   12.543%   $86.5906   $86.59   $86.60   $86.60  
  Purchase #7 $164.46   8.444%   $178.347   $178.35   $178.35   $178.30  
  7 purchase totals = $678.42       $743.2137   $743.22   $743.20   $743.10