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 $198.35   8.852%   $215.9079   $215.91   $215.90   $215.90  
  Purchase #2 $127.81   5.608%   $134.9776   $134.98   $135.00   $135.00  
  Purchase #3 $86.75   9.533%   $95.0199   $95.02   $95.00   $95.00  
  Purchase #4 $189.47   7.153%   $203.0228   $203.02   $203.00   $203.00  
  Purchase #5 $246.40   8.109%   $266.3806   $266.38   $266.40   $266.40  
  Purchase #6 $130.78   5.299%   $137.71   $137.71   $137.70   $137.70  
  Purchase #7 $30.99   11.446%   $34.5371   $34.54   $34.55   $34.50  
  7 purchase totals = $1,010.55       $1,087.5559   $1,087.56   $1,087.55   $1,087.50