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 $49.42   13.589%   $56.1357   $56.14   $56.15   $56.10  
  Purchase #2 $220.64   6.637%   $235.2839   $235.28   $235.30   $235.30  
  Purchase #3 $64.76   4.832%   $67.8892   $67.89   $67.90   $67.90  
  Purchase #4 $250.68   9.850%   $275.372   $275.37   $275.35   $275.40  
  Purchase #5 $87.38   12.226%   $98.0631   $98.06   $98.05   $98.10  
  Purchase #6 $81.72   4.333%   $85.2609   $85.26   $85.25   $85.30  
  Purchase #7 $189.72   10.685%   $209.9916   $209.99   $210.00   $210.00  
  7 purchase totals = $944.32       $1,027.9964   $1,027.99   $1,028.00   $1,028.10