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 $36.58   12.731%   $41.237   $41.24   $41.25   $41.20  
  Purchase #2 $113.83   5.503%   $120.0941   $120.09   $120.10   $120.10  
  Purchase #3 $115.37   7.740%   $124.2996   $124.30   $124.30   $124.30  
  Purchase #4 $10.60   9.522%   $11.6093   $11.61   $11.60   $11.60  
  Purchase #5 $50.93   5.376%   $53.668   $53.67   $53.65   $53.70  
  Purchase #6 $97.95   5.546%   $103.3823   $103.38   $103.40   $103.40  
  Purchase #7 $247.28   3.116%   $254.9852   $254.99   $255.00   $255.00  
  7 purchase totals = $672.54       $709.2755   $709.28   $709.30   $709.30