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 $73.76   13.688%   $83.8563   $83.86   $83.85   $83.90  
  Purchase #2 $55.86   8.395%   $60.5494   $60.55   $60.55   $60.50  
  Purchase #3 $35.76   5.779%   $37.8266   $37.83   $37.85   $37.80  
  Purchase #4 $136.66   8.112%   $147.7459   $147.75   $147.75   $147.70  
  Purchase #5 $199.83   12.290%   $224.3891   $224.39   $224.40   $224.40  
  Purchase #6 $65.38   10.522%   $72.2593   $72.26   $72.25   $72.30  
  Purchase #7 $238.38   12.436%   $268.0249   $268.02   $268.00   $268.00  
  7 purchase totals = $805.63       $894.6515   $894.66   $894.65   $894.60