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 $233.91   11.694%   $261.2634   $261.26   $261.25   $261.30  
  Purchase #2 $48.54   7.296%   $52.0815   $52.08   $52.10   $52.10  
  Purchase #3 $138.63   11.832%   $155.0327   $155.03   $155.05   $155.00  
  Purchase #4 $55.54   12.304%   $62.3736   $62.37   $62.35   $62.40  
  Purchase #5 $57.64   5.225%   $60.6517   $60.65   $60.65   $60.70  
  Purchase #6 $9.29   11.795%   $10.3858   $10.39   $10.40   $10.40  
  Purchase #7 $205.80   4.379%   $214.812   $214.81   $214.80   $214.80  
  7 purchase totals = $749.35       $816.6007   $816.59   $816.60   $816.70