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 $141.66   3.746%   $146.9666   $146.97   $146.95   $147.00  
  Purchase #2 $111.85   10.155%   $123.2084   $123.21   $123.20   $123.20  
  Purchase #3 $55.37   6.483%   $58.9596   $58.96   $58.95   $59.00  
  Purchase #4 $218.69   13.434%   $248.0688   $248.07   $248.05   $248.10  
  Purchase #5 $65.76   12.727%   $74.1293   $74.13   $74.15   $74.10  
  Purchase #6 $37.93   11.403%   $42.2552   $42.26   $42.25   $42.30  
  Purchase #7 $169.64   3.334%   $175.2958   $175.30   $175.30   $175.30  
  7 purchase totals = $800.90       $868.8837   $868.90   $868.85   $869.00