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 $67.71   4.338%   $70.6473   $70.65   $70.65   $70.60  
  Purchase #2 $74.29   9.798%   $81.5689   $81.57   $81.55   $81.60  
  Purchase #3 $26.50   13.659%   $30.1196   $30.12   $30.10   $30.10  
  Purchase #4 $223.94   9.812%   $245.913   $245.91   $245.90   $245.90  
  Purchase #5 $68.36   9.752%   $75.0265   $75.03   $75.05   $75.00  
  Purchase #6 $229.38   12.323%   $257.6465   $257.65   $257.65   $257.60  
  Purchase #7 $14.75   4.580%   $15.4256   $15.43   $15.45   $15.40  
  7 purchase totals = $704.93       $776.3474   $776.36   $776.35   $776.20