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 $164.29   11.339%   $182.9188   $182.92   $182.90   $182.90  
  Purchase #2 $210.53   7.689%   $226.7177   $226.72   $226.70   $226.70  
  Purchase #3 $46.83   6.132%   $49.7016   $49.70   $49.70   $49.70  
  Purchase #4 $123.37   11.179%   $137.1615   $137.16   $137.15   $137.20  
  Purchase #5 $28.86   4.783%   $30.2404   $30.24   $30.25   $30.20  
  Purchase #6 $8.52   12.773%   $9.6083   $9.61   $9.60   $9.60  
  Purchase #7 $185.26   11.758%   $207.0429   $207.04   $207.05   $207.00  
  7 purchase totals = $767.66       $843.3912   $843.39   $843.35   $843.30