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 $54.90   12.152%   $61.5714   $61.57   $61.55   $61.60  
  Purchase #2 $69.40   9.651%   $76.0978   $76.10   $76.10   $76.10  
  Purchase #3 $67.87   11.611%   $75.7504   $75.75   $75.75   $75.80  
  Purchase #4 $116.61   13.863%   $132.7756   $132.78   $132.80   $132.80  
  Purchase #5 $164.75   7.490%   $177.0898   $177.09   $177.10   $177.10  
  Purchase #6 $225.82   4.437%   $235.8396   $235.84   $235.85   $235.80  
  Purchase #7 $214.71   10.269%   $236.7586   $236.76   $236.75   $236.80  
  7 purchase totals = $914.06       $995.8832   $995.89   $995.90   $996.00