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 $53.78   5.509%   $56.7427   $56.74   $56.75   $56.70  
  Purchase #2 $235.56   7.203%   $252.5274   $252.53   $252.55   $252.50  
  Purchase #3 $23.67   9.660%   $25.9565   $25.96   $25.95   $26.00  
  Purchase #4 $177.96   8.287%   $192.7075   $192.71   $192.70   $192.70  
  Purchase #5 $90.65   11.600%   $101.1654   $101.17   $101.15   $101.20  
  Purchase #6 $105.81   11.221%   $117.6829   $117.68   $117.70   $117.70  
  Purchase #7 $250.90   5.197%   $263.9393   $263.94   $263.95   $263.90  
  7 purchase totals = $938.33       $1,010.7217   $1,010.73   $1,010.75   $1,010.70