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 $246.99   8.166%   $267.1592   $267.16   $267.15   $267.20  
  Purchase #2 $94.89   10.329%   $104.6912   $104.69   $104.70   $104.70  
  Purchase #3 $122.25   10.791%   $135.442   $135.44   $135.45   $135.40  
  Purchase #4 $239.65   12.469%   $269.532   $269.53   $269.55   $269.50  
  Purchase #5 $39.35   12.835%   $44.4006   $44.40   $44.40   $44.40  
  Purchase #6 $211.79   11.289%   $235.699   $235.70   $235.70   $235.70  
  Purchase #7 $98.99   4.105%   $103.0535   $103.05   $103.05   $103.10  
  7 purchase totals = $1,053.91       $1,159.9775   $1,159.97   $1,160.00   $1,160.00