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 $156.38   5.552%   $165.0622   $165.06   $165.05   $165.10  
  Purchase #2 $100.78   10.217%   $111.0767   $111.08   $111.10   $111.10  
  Purchase #3 $42.72   3.277%   $44.1199   $44.12   $44.10   $44.10  
  Purchase #4 $198.31   6.745%   $211.686   $211.69   $211.70   $211.70  
  Purchase #5 $195.53   4.458%   $204.2467   $204.25   $204.25   $204.20  
  Purchase #6 $61.80   11.493%   $68.9027   $68.90   $68.90   $68.90  
  Purchase #7 $210.47   5.116%   $221.2376   $221.24   $221.25   $221.20  
  7 purchase totals = $965.99       $1,026.3318   $1,026.34   $1,026.35   $1,026.30