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 $192.61   13.715%   $219.0265   $219.03   $219.05   $219.00  
  Purchase #2 $139.52   9.368%   $152.5902   $152.59   $152.60   $152.60  
  Purchase #3 $113.27   12.329%   $127.2351   $127.24   $127.25   $127.20  
  Purchase #4 $202.63   13.255%   $229.4886   $229.49   $229.50   $229.50  
  Purchase #5 $58.91   6.611%   $62.8045   $62.80   $62.80   $62.80  
  Purchase #6 $221.52   6.630%   $236.2068   $236.21   $236.20   $236.20  
  Purchase #7 $149.68   5.241%   $157.5247   $157.52   $157.50   $157.50  
  7 purchase totals = $1,078.14       $1,184.8764   $1,184.88   $1,184.90   $1,184.80