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 $162.47   12.833%   $183.3198   $183.32   $183.30   $183.30  
  Purchase #2 $31.35   6.834%   $33.4925   $33.49   $33.50   $33.50  
  Purchase #3 $38.52   10.544%   $42.5815   $42.58   $42.60   $42.60  
  Purchase #4 $148.98   9.704%   $163.437   $163.44   $163.45   $163.40  
  Purchase #5 $97.91   3.166%   $101.0098   $101.01   $101.00   $101.00  
  Purchase #6 $155.64   13.188%   $176.1658   $176.17   $176.15   $176.20  
  Purchase #7 $237.92   13.475%   $269.9797   $269.98   $270.00   $270.00  
  7 purchase totals = $872.79       $969.9861   $969.99   $970.00   $970.00