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 $54.65   5.589%   $57.7044   $57.70   $57.70   $57.70  
  Purchase #2 $46.88   8.257%   $50.7509   $50.75   $50.75   $50.80  
  Purchase #3 $209.95   3.451%   $217.1954   $217.20   $217.20   $217.20  
  Purchase #4 $68.30   13.264%   $77.3593   $77.36   $77.35   $77.40  
  Purchase #5 $221.86   6.851%   $237.0596   $237.06   $237.05   $237.10  
  Purchase #6 $50.83   9.759%   $55.7905   $55.79   $55.80   $55.80  
  Purchase #7 $33.82   4.730%   $35.4197   $35.42   $35.40   $35.40  
  7 purchase totals = $686.29       $731.2798   $731.28   $731.25   $731.40