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 $39.28   13.522%   $44.5914   $44.59   $44.60   $44.60  
  Purchase #2 $103.73   13.401%   $117.6309   $117.63   $117.65   $117.60  
  Purchase #3 $92.99   3.526%   $96.2688   $96.27   $96.25   $96.30  
  Purchase #4 $221.60   10.396%   $244.6375   $244.64   $244.65   $244.60  
  Purchase #5 $61.70   12.751%   $69.5674   $69.57   $69.55   $69.60  
  Purchase #6 $64.50   4.269%   $67.2535   $67.25   $67.25   $67.30  
  Purchase #7 $192.50   9.642%   $211.0609   $211.06   $211.05   $211.10  
  7 purchase totals = $776.30       $851.0104   $851.01   $851.00   $851.10