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 $230.30   10.552%   $254.6013   $254.60   $254.60   $254.60  
  Purchase #2 $188.92   8.783%   $205.5128   $205.51   $205.50   $205.50  
  Purchase #3 $25.96   8.160%   $28.0783   $28.08   $28.10   $28.10  
  Purchase #4 $193.41   6.786%   $206.5348   $206.53   $206.55   $206.50  
  Purchase #5 $27.82   8.489%   $30.1816   $30.18   $30.20   $30.20  
  Purchase #6 $70.34   6.168%   $74.6786   $74.68   $74.70   $74.70  
  Purchase #7 $206.89   8.577%   $224.635   $224.64   $224.65   $224.60  
  7 purchase totals = $943.64       $1,024.2224   $1,024.22   $1,024.30   $1,024.20