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 $53.76   4.187%   $56.0109   $56.01   $56.00   $56.00  
  Purchase #2 $158.98   11.763%   $177.6808   $177.68   $177.70   $177.70  
  Purchase #3 $241.26   4.192%   $251.3736   $251.37   $251.35   $251.40  
  Purchase #4 $131.69   7.265%   $141.2573   $141.26   $141.25   $141.30  
  Purchase #5 $111.65   10.703%   $123.5999   $123.60   $123.60   $123.60  
  Purchase #6 $115.73   10.119%   $127.4407   $127.44   $127.45   $127.40  
  Purchase #7 $105.73   3.305%   $109.2244   $109.22   $109.20   $109.20  
  7 purchase totals = $918.80       $986.5876   $986.58   $986.55   $986.60