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 $112.93   10.724%   $125.0406   $125.04   $125.05   $125.00  
  Purchase #2 $208.53   11.651%   $232.8258   $232.83   $232.85   $232.80  
  Purchase #3 $64.30   7.856%   $69.3514   $69.35   $69.35   $69.40  
  Purchase #4 $223.62   6.295%   $237.6969   $237.70   $237.70   $237.70  
  Purchase #5 $183.91   12.109%   $206.1797   $206.18   $206.20   $206.20  
  Purchase #6 $143.87   8.727%   $156.4255   $156.43   $156.45   $156.40  
  Purchase #7 $65.73   8.769%   $71.4939   $71.49   $71.50   $71.50  
  7 purchase totals = $1,002.89       $1,099.0138   $1,099.02   $1,099.10   $1,099.00