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 $67.92   13.767%   $77.2705   $77.27   $77.25   $77.30  
  Purchase #2 $58.48   7.444%   $62.8333   $62.83   $62.85   $62.80  
  Purchase #3 $184.66   3.527%   $191.173   $191.17   $191.15   $191.20  
  Purchase #4 $39.90   7.833%   $43.0254   $43.03   $43.05   $43.00  
  Purchase #5 $173.51   10.308%   $191.3954   $191.40   $191.40   $191.40  
  Purchase #6 $234.99   11.384%   $261.7413   $261.74   $261.75   $261.70  
  Purchase #7 $24.30   3.443%   $25.1366   $25.14   $25.15   $25.10  
  7 purchase totals = $783.76       $852.5755   $852.58   $852.60   $852.50