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 $52.36   8.782%   $56.9583   $56.96   $56.95   $57.00  
  Purchase #2 $63.65   3.786%   $66.0598   $66.06   $66.05   $66.10  
  Purchase #3 $87.31   12.232%   $97.9898   $97.99   $98.00   $98.00  
  Purchase #4 $114.79   6.206%   $121.9139   $121.91   $121.90   $121.90  
  Purchase #5 $20.76   7.108%   $22.2356   $22.24   $22.25   $22.20  
  Purchase #6 $107.37   10.481%   $118.6234   $118.62   $118.60   $118.60  
  Purchase #7 $69.98   10.265%   $77.1634   $77.16   $77.15   $77.20  
  7 purchase totals = $516.22       $560.9442   $560.94   $560.90   $561.00