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 $62.44   8.261%   $67.5982   $67.60   $67.60   $67.60  
  Purchase #2 $44.52   9.864%   $48.9115   $48.91   $48.90   $48.90  
  Purchase #3 $187.36   3.196%   $193.348   $193.35   $193.35   $193.30  
  Purchase #4 $90.76   7.312%   $97.3964   $97.40   $97.40   $97.40  
  Purchase #5 $17.64   3.420%   $18.2433   $18.24   $18.25   $18.20  
  Purchase #6 $167.34   4.368%   $174.6494   $174.65   $174.65   $174.60  
  Purchase #7 $92.70   6.327%   $98.5651   $98.57   $98.55   $98.60  
  7 purchase totals = $662.76       $698.7119   $698.72   $698.70   $698.60