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 $193.35   13.143%   $218.762   $218.76   $218.75   $218.80  
  Purchase #2 $104.26   11.233%   $115.9715   $115.97   $115.95   $116.00  
  Purchase #3 $127.59   10.565%   $141.0699   $141.07   $141.05   $141.10  
  Purchase #4 $151.65   7.826%   $163.5181   $163.52   $163.50   $163.50  
  Purchase #5 $30.53   13.856%   $34.7602   $34.76   $34.75   $34.80  
  Purchase #6 $142.73   11.760%   $159.515   $159.52   $159.50   $159.50  
  Purchase #7 $42.46   8.436%   $46.0419   $46.04   $46.05   $46.00  
  7 purchase totals = $792.57       $879.6386   $879.64   $879.55   $879.70