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 $138.49   5.536%   $146.1568   $146.16   $146.15   $146.20  
  Purchase #2 $23.36   11.665%   $26.0849   $26.08   $26.10   $26.10  
  Purchase #3 $54.57   12.199%   $61.227   $61.23   $61.25   $61.20  
  Purchase #4 $238.56   10.478%   $263.5563   $263.56   $263.55   $263.60  
  Purchase #5 $117.76   12.548%   $132.5365   $132.54   $132.55   $132.50  
  Purchase #6 $104.99   4.348%   $109.555   $109.56   $109.55   $109.60  
  Purchase #7 $20.59   7.258%   $22.0844   $22.08   $22.10   $22.10  
  7 purchase totals = $698.32       $761.2009   $761.21   $761.25   $761.30