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 $69.34   3.164%   $71.5339   $71.53   $71.55   $71.50  
  Purchase #2 $185.46   8.717%   $201.6265   $201.63   $201.65   $201.60  
  Purchase #3 $226.53   3.816%   $235.1744   $235.17   $235.15   $235.20  
  Purchase #4 $223.54   6.774%   $238.6826   $238.68   $238.70   $238.70  
  Purchase #5 $83.73   12.271%   $94.0045   $94.00   $94.00   $94.00  
  Purchase #6 $19.72   9.768%   $21.6462   $21.65   $21.65   $21.60  
  Purchase #7 $48.95   3.493%   $50.6598   $50.66   $50.65   $50.70  
  7 purchase totals = $857.27       $913.3279   $913.32   $913.35   $913.30