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 $118.97   6.389%   $126.571   $126.57   $126.55   $126.60  
  Purchase #2 $177.81   3.631%   $184.2663   $184.27   $184.25   $184.30  
  Purchase #3 $96.75   7.161%   $103.6783   $103.68   $103.70   $103.70  
  Purchase #4 $114.95   8.376%   $124.5782   $124.58   $124.60   $124.60  
  Purchase #5 $99.58   11.544%   $111.0755   $111.08   $111.10   $111.10  
  Purchase #6 $149.58   4.566%   $156.4098   $156.41   $156.40   $156.40  
  Purchase #7 $185.82   3.167%   $191.7049   $191.70   $191.70   $191.70  
  7 purchase totals = $943.46       $998.2840   $998.29   $998.30   $998.40