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 $62.97   12.131%   $70.6089   $70.61   $70.60   $70.60  
  Purchase #2 $118.85   4.631%   $124.3539   $124.35   $124.35   $124.40  
  Purchase #3 $216.30   9.321%   $236.4613   $236.46   $236.45   $236.50  
  Purchase #4 $142.42   9.869%   $156.4754   $156.48   $156.50   $156.50  
  Purchase #5 $77.81   4.621%   $81.4056   $81.41   $81.40   $81.40  
  Purchase #6 $113.37   7.829%   $122.2457   $122.25   $122.25   $122.20  
  Purchase #7 $248.82   9.762%   $273.1098   $273.11   $273.10   $273.10  
  7 purchase totals = $980.54       $1,064.6606   $1,064.67   $1,064.65   $1,064.70