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 $246.44   10.247%   $271.6927   $271.69   $271.70   $271.70  
  Purchase #2 $60.66   12.760%   $68.4002   $68.40   $68.40   $68.40  
  Purchase #3 $27.80   8.530%   $30.1713   $30.17   $30.15   $30.20  
  Purchase #4 $131.80   11.564%   $147.0414   $147.04   $147.05   $147.00  
  Purchase #5 $172.46   13.311%   $195.4162   $195.42   $195.40   $195.40  
  Purchase #6 $242.71   5.316%   $255.6125   $255.61   $255.60   $255.60  
  Purchase #7 $53.90   4.782%   $56.4775   $56.48   $56.50   $56.50  
  7 purchase totals = $935.77       $1,024.8118   $1,024.81   $1,024.80   $1,024.80