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 $247.59   8.518%   $268.6797   $268.68   $268.70   $268.70  
  Purchase #2 $159.37   3.294%   $164.6196   $164.62   $164.60   $164.60  
  Purchase #3 $102.53   10.549%   $113.3459   $113.35   $113.35   $113.30  
  Purchase #4 $104.26   13.306%   $118.1328   $118.13   $118.15   $118.10  
  Purchase #5 $17.62   7.863%   $19.0055   $19.01   $19.00   $19.00  
  Purchase #6 $150.80   3.860%   $156.6209   $156.62   $156.60   $156.60  
  Purchase #7 $183.66   4.259%   $191.4821   $191.48   $191.50   $191.50  
  7 purchase totals = $965.83       $1,031.8865   $1,031.89   $1,031.90   $1,031.80