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 $118.87   6.539%   $126.6429   $126.64   $126.65   $126.60  
  Purchase #2 $21.83   7.780%   $23.5284   $23.53   $23.55   $23.50  
  Purchase #3 $155.40   3.332%   $160.5779   $160.58   $160.60   $160.60  
  Purchase #4 $7.69   7.502%   $8.2669   $8.27   $8.25   $8.30  
  Purchase #5 $238.55   8.768%   $259.4661   $259.47   $259.45   $259.50  
  Purchase #6 $124.38   5.518%   $131.2433   $131.24   $131.25   $131.20  
  Purchase #7 $244.56   5.222%   $257.3309   $257.33   $257.35   $257.30  
  7 purchase totals = $911.28       $967.0564   $967.06   $967.10   $967.00