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 $208.83   5.663%   $220.656   $220.66   $220.65   $220.70  
  Purchase #2 $158.80   6.128%   $168.5313   $168.53   $168.55   $168.50  
  Purchase #3 $168.93   13.554%   $191.8268   $191.83   $191.85   $191.80  
  Purchase #4 $231.81   8.796%   $252.2   $252.20   $252.20   $252.20  
  Purchase #5 $194.59   10.214%   $214.4654   $214.47   $214.45   $214.50  
  Purchase #6 $24.39   5.797%   $25.8039   $25.80   $25.80   $25.80  
  Purchase #7 $205.37   7.356%   $220.477   $220.48   $220.50   $220.50  
  7 purchase totals = $1,192.72       $1,293.9604   $1,293.97   $1,294.00   $1,294.00