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 $55.54   5.467%   $58.5764   $58.58   $58.60   $58.60  
  Purchase #2 $177.35   6.123%   $188.2091   $188.21   $188.20   $188.20  
  Purchase #3 $103.74   5.435%   $109.3783   $109.38   $109.40   $109.40  
  Purchase #4 $207.99   13.491%   $236.0499   $236.05   $236.05   $236.00  
  Purchase #5 $25.58   3.708%   $26.5285   $26.53   $26.55   $26.50  
  Purchase #6 $135.83   10.153%   $149.6208   $149.62   $149.60   $149.60  
  Purchase #7 $208.65   12.612%   $234.9649   $234.96   $234.95   $235.00  
  7 purchase totals = $914.68       $1,003.3279   $1,003.33   $1,003.35   $1,003.30