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 $51.28   10.369%   $56.5972   $56.60   $56.60   $56.60  
  Purchase #2 $117.51   4.662%   $122.9883   $122.99   $123.00   $123.00  
  Purchase #3 $101.80   11.285%   $113.2881   $113.29   $113.30   $113.30  
  Purchase #4 $214.54   9.377%   $234.6574   $234.66   $234.65   $234.70  
  Purchase #5 $161.60   12.822%   $182.3204   $182.32   $182.30   $182.30  
  Purchase #6 $145.79   6.719%   $155.5856   $155.59   $155.60   $155.60  
  Purchase #7 $25.25   7.716%   $27.1983   $27.20   $27.20   $27.20  
  7 purchase totals = $817.77       $892.6353   $892.65   $892.65   $892.70