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 $236.87   13.600%   $269.0843   $269.08   $269.10   $269.10  
  Purchase #2 $225.52   6.269%   $239.6578   $239.66   $239.65   $239.70  
  Purchase #3 $146.89   3.563%   $152.1237   $152.12   $152.10   $152.10  
  Purchase #4 $56.76   6.457%   $60.425   $60.43   $60.45   $60.40  
  Purchase #5 $42.84   9.461%   $46.8931   $46.89   $46.90   $46.90  
  Purchase #6 $216.70   4.455%   $226.354   $226.35   $226.35   $226.40  
  Purchase #7 $233.46   4.284%   $243.4614   $243.46   $243.45   $243.50  
  7 purchase totals = $1,159.04       $1,237.9993   $1,237.99   $1,238.00   $1,238.10