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 $241.52   11.679%   $269.7271   $269.73   $269.75   $269.70  
  Purchase #2 $114.91   6.235%   $122.0746   $122.07   $122.05   $122.10  
  Purchase #3 $77.99   11.693%   $87.1094   $87.11   $87.10   $87.10  
  Purchase #4 $231.40   13.217%   $261.9841   $261.98   $262.00   $262.00  
  Purchase #5 $25.79   6.698%   $27.5174   $27.52   $27.50   $27.50  
  Purchase #6 $94.42   11.861%   $105.6192   $105.62   $105.60   $105.60  
  Purchase #7 $154.45   13.778%   $175.7301   $175.73   $175.75   $175.70  
  7 purchase totals = $940.48       $1,049.7619   $1,049.76   $1,049.75   $1,049.70