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 $127.38   12.613%   $143.4464   $143.45   $143.45   $143.40  
  Purchase #2 $201.72   3.615%   $209.0122   $209.01   $209.00   $209.00  
  Purchase #3 $109.48   13.277%   $124.0157   $124.02   $124.00   $124.00  
  Purchase #4 $63.65   12.705%   $71.7367   $71.74   $71.75   $71.70  
  Purchase #5 $234.36   5.512%   $247.2779   $247.28   $247.30   $247.30  
  Purchase #6 $144.66   8.445%   $156.8765   $156.88   $156.90   $156.90  
  Purchase #7 $94.45   4.379%   $98.586   $98.59   $98.60   $98.60  
  7 purchase totals = $975.70       $1,050.9514   $1,050.97   $1,051.00   $1,050.90