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 $114.25   11.626%   $127.5327   $127.53   $127.55   $127.50  
  Purchase #2 $208.48   10.243%   $229.8346   $229.83   $229.85   $229.80  
  Purchase #3 $235.86   10.844%   $261.4367   $261.44   $261.45   $261.40  
  Purchase #4 $164.50   6.417%   $175.056   $175.06   $175.05   $175.10  
  Purchase #5 $117.52   13.166%   $132.9927   $132.99   $133.00   $133.00  
  Purchase #6 $209.72   8.191%   $226.8982   $226.90   $226.90   $226.90  
  Purchase #7 $197.58   13.480%   $224.2138   $224.21   $224.20   $224.20  
  7 purchase totals = $1,247.91       $1,377.9647   $1,377.96   $1,378.00   $1,377.90