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 $185.95   8.317%   $201.4155   $201.42   $201.40   $201.40  
  Purchase #2 $27.53   3.856%   $28.5916   $28.59   $28.60   $28.60  
  Purchase #3 $110.92   10.857%   $122.9626   $122.96   $122.95   $123.00  
  Purchase #4 $32.59   10.161%   $35.9015   $35.90   $35.90   $35.90  
  Purchase #5 $86.53   11.587%   $96.5562   $96.56   $96.55   $96.60  
  Purchase #6 $164.85   4.635%   $172.4908   $172.49   $172.50   $172.50  
  Purchase #7 $115.78   11.422%   $129.0044   $129.00   $129.00   $129.00  
  7 purchase totals = $724.15       $786.9226   $786.92   $786.90   $787.00