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 $219.72   13.210%   $248.745   $248.75   $248.75   $248.70  
  Purchase #2 $92.26   5.788%   $97.6   $97.60   $97.60   $97.60  
  Purchase #3 $126.36   12.629%   $142.318   $142.32   $142.30   $142.30  
  Purchase #4 $111.84   7.504%   $120.2325   $120.23   $120.25   $120.20  
  Purchase #5 $186.31   7.657%   $200.5758   $200.58   $200.60   $200.60  
  Purchase #6 $40.65   3.728%   $42.1654   $42.17   $42.15   $42.20  
  Purchase #7 $84.93   5.615%   $89.6988   $89.70   $89.70   $89.70  
  7 purchase totals = $862.07       $941.3355   $941.35   $941.35   $941.30