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 $22.52   9.564%   $24.6738   $24.67   $24.65   $24.70  
  Purchase #2 $179.50   3.509%   $185.7987   $185.80   $185.80   $185.80  
  Purchase #3 $226.72   8.649%   $246.329   $246.33   $246.35   $246.30  
  Purchase #4 $234.80   3.842%   $243.821   $243.82   $243.80   $243.80  
  Purchase #5 $61.51   6.451%   $65.478   $65.48   $65.50   $65.50  
  Purchase #6 $58.79   10.209%   $64.7919   $64.79   $64.80   $64.80  
  Purchase #7 $208.26   13.639%   $236.6646   $236.66   $236.65   $236.70  
  7 purchase totals = $992.10       $1,067.5570   $1,067.55   $1,067.55   $1,067.60