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 $61.76   12.110%   $69.2391   $69.24   $69.25   $69.20  
  Purchase #2 $77.34   4.383%   $80.7298   $80.73   $80.75   $80.70  
  Purchase #3 $183.65   4.771%   $192.4119   $192.41   $192.40   $192.40  
  Purchase #4 $139.88   5.291%   $147.2811   $147.28   $147.30   $147.30  
  Purchase #5 $68.86   12.343%   $77.3594   $77.36   $77.35   $77.40  
  Purchase #6 $206.53   3.345%   $213.4384   $213.44   $213.45   $213.40  
  Purchase #7 $162.61   5.262%   $171.1665   $171.17   $171.15   $171.20  
  7 purchase totals = $900.63       $951.6262   $951.63   $951.65   $951.60