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 $188.83   9.837%   $207.4052   $207.41   $207.40   $207.40  
  Purchase #2 $95.60   6.785%   $102.0865   $102.09   $102.10   $102.10  
  Purchase #3 $34.40   6.812%   $36.7433   $36.74   $36.75   $36.70  
  Purchase #4 $229.73   7.501%   $246.962   $246.96   $246.95   $247.00  
  Purchase #5 $101.97   9.335%   $111.4889   $111.49   $111.50   $111.50  
  Purchase #6 $94.36   13.688%   $107.276   $107.28   $107.30   $107.30  
  Purchase #7 $70.81   3.683%   $73.4179   $73.42   $73.40   $73.40  
  7 purchase totals = $815.70       $885.3798   $885.39   $885.40   $885.40