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 $10.61   13.213%   $12.0119   $12.01   $12.00   $12.00  
  Purchase #2 $31.36   12.674%   $35.3346   $35.33   $35.35   $35.30  
  Purchase #3 $55.50   11.142%   $61.6838   $61.68   $61.70   $61.70  
  Purchase #4 $42.82   8.195%   $46.3291   $46.33   $46.35   $46.30  
  Purchase #5 $242.72   5.432%   $255.9046   $255.90   $255.90   $255.90  
  Purchase #6 $71.39   10.613%   $78.9666   $78.97   $78.95   $79.00  
  Purchase #7 $68.68   7.719%   $73.9814   $73.98   $74.00   $74.00  
  7 purchase totals = $523.08       $564.2120   $564.20   $564.25   $564.20