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 $246.96   10.705%   $273.3971   $273.40   $273.40   $273.40  
  Purchase #2 $31.71   7.750%   $34.1675   $34.17   $34.15   $34.20  
  Purchase #3 $13.58   3.843%   $14.1019   $14.10   $14.10   $14.10  
  Purchase #4 $160.69   10.274%   $177.1993   $177.20   $177.20   $177.20  
  Purchase #5 $61.65   5.258%   $64.8916   $64.89   $64.90   $64.90  
  Purchase #6 $246.57   6.552%   $262.7253   $262.73   $262.75   $262.70  
  Purchase #7 $213.26   13.810%   $242.7112   $242.71   $242.70   $242.70  
  7 purchase totals = $974.42       $1,069.1939   $1,069.20   $1,069.20   $1,069.20