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 $228.43   6.684%   $243.6983   $243.70   $243.70   $243.70  
  Purchase #2 $114.72   8.344%   $124.2922   $124.29   $124.30   $124.30  
  Purchase #3 $113.28   9.315%   $123.832   $123.83   $123.85   $123.80  
  Purchase #4 $244.95   6.754%   $261.4939   $261.49   $261.50   $261.50  
  Purchase #5 $231.92   7.587%   $249.5158   $249.52   $249.50   $249.50  
  Purchase #6 $146.70   7.327%   $157.4487   $157.45   $157.45   $157.40  
  Purchase #7 $7.35   4.624%   $7.6899   $7.69   $7.70   $7.70  
  7 purchase totals = $1,087.35       $1,167.9708   $1,167.97   $1,168.00   $1,167.90