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 $24.81   3.407%   $25.6553   $25.66   $25.65   $25.70  
  Purchase #2 $239.64   7.508%   $257.6322   $257.63   $257.65   $257.60  
  Purchase #3 $214.51   8.161%   $232.0162   $232.02   $232.00   $232.00  
  Purchase #4 $182.72   5.162%   $192.152   $192.15   $192.15   $192.20  
  Purchase #5 $188.53   13.866%   $214.6716   $214.67   $214.65   $214.70  
  Purchase #6 $236.88   5.241%   $249.2949   $249.29   $249.30   $249.30  
  Purchase #7 $38.83   7.626%   $41.7912   $41.79   $41.80   $41.80  
  7 purchase totals = $1,125.92       $1,213.2134   $1,213.21   $1,213.20   $1,213.30