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 $94.62   11.563%   $105.5609   $105.56   $105.55   $105.60  
  Purchase #2 $207.85   13.705%   $236.3358   $236.34   $236.35   $236.30  
  Purchase #3 $60.54   3.828%   $62.8575   $62.86   $62.85   $62.90  
  Purchase #4 $247.48   10.647%   $273.8292   $273.83   $273.85   $273.80  
  Purchase #5 $69.41   11.630%   $77.4824   $77.48   $77.50   $77.50  
  Purchase #6 $247.80   13.874%   $282.1798   $282.18   $282.20   $282.20  
  Purchase #7 $18.75   3.589%   $19.4229   $19.42   $19.40   $19.40  
  7 purchase totals = $946.45       $1,057.6685   $1,057.67   $1,057.70   $1,057.70