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 $163.99   13.816%   $186.6469   $186.65   $186.65   $186.60  
  Purchase #2 $48.72   8.155%   $52.6931   $52.69   $52.70   $52.70  
  Purchase #3 $136.35   11.724%   $152.3357   $152.34   $152.35   $152.30  
  Purchase #4 $49.90   11.771%   $55.7737   $55.77   $55.75   $55.80  
  Purchase #5 $222.81   8.674%   $242.1365   $242.14   $242.15   $242.10  
  Purchase #6 $113.90   8.844%   $123.9733   $123.97   $123.95   $124.00  
  Purchase #7 $233.98   9.342%   $255.8384   $255.84   $255.85   $255.80  
  7 purchase totals = $969.65       $1,069.3976   $1,069.40   $1,069.40   $1,069.30