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 $53.82   4.518%   $56.2516   $56.25   $56.25   $56.30  
  Purchase #2 $222.93   5.253%   $234.6405   $234.64   $234.65   $234.60  
  Purchase #3 $149.78   3.754%   $155.4027   $155.40   $155.40   $155.40  
  Purchase #4 $129.70   7.282%   $139.1448   $139.14   $139.15   $139.10  
  Purchase #5 $42.32   10.156%   $46.618   $46.62   $46.60   $46.60  
  Purchase #6 $186.88   7.547%   $200.9838   $200.98   $201.00   $201.00  
  Purchase #7 $31.46   8.816%   $34.2335   $34.23   $34.25   $34.20  
  7 purchase totals = $816.89       $867.2749   $867.26   $867.30   $867.20