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 $237.33   13.286%   $268.8617   $268.86   $268.85   $268.90  
  Purchase #2 $106.45   12.684%   $119.9521   $119.95   $119.95   $120.00  
  Purchase #3 $94.62   5.169%   $99.5109   $99.51   $99.50   $99.50  
  Purchase #4 $154.65   12.680%   $174.2596   $174.26   $174.25   $174.30  
  Purchase #5 $208.26   11.356%   $231.91   $231.91   $231.90   $231.90  
  Purchase #6 $248.88   12.538%   $280.0846   $280.08   $280.10   $280.10  
  Purchase #7 $46.80   11.671%   $52.262   $52.26   $52.25   $52.30  
  7 purchase totals = $1,096.99       $1,226.8409   $1,226.83   $1,226.80   $1,227.00