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 $236.75   7.504%   $254.5157   $254.52   $254.50   $254.50  
  Purchase #2 $222.67   13.232%   $252.1337   $252.13   $252.15   $252.10  
  Purchase #3 $46.57   11.633%   $51.9875   $51.99   $52.00   $52.00  
  Purchase #4 $193.27   7.703%   $208.1576   $208.16   $208.15   $208.20  
  Purchase #5 $182.70   7.164%   $195.7886   $195.79   $195.80   $195.80  
  Purchase #6 $231.71   3.492%   $239.8013   $239.80   $239.80   $239.80  
  Purchase #7 $234.28   10.711%   $259.3737   $259.37   $259.35   $259.40  
  7 purchase totals = $1,347.95       $1,461.7581   $1,461.76   $1,461.75   $1,461.80