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 $14.69   10.278%   $16.1998   $16.20   $16.20   $16.20  
  Purchase #2 $185.40   11.652%   $207.0028   $207.00   $207.00   $207.00  
  Purchase #3 $43.60   12.148%   $48.8965   $48.90   $48.90   $48.90  
  Purchase #4 $85.71   11.511%   $95.5761   $95.58   $95.60   $95.60  
  Purchase #5 $130.27   13.313%   $147.6128   $147.61   $147.60   $147.60  
  Purchase #6 $209.35   12.474%   $235.4643   $235.46   $235.45   $235.50  
  Purchase #7 $32.60   7.861%   $35.1627   $35.16   $35.15   $35.20  
  7 purchase totals = $701.62       $785.9150   $785.91   $785.90   $786.00