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 $224.61   6.412%   $239.012   $239.01   $239.00   $239.00  
  Purchase #2 $61.61   13.139%   $69.7049   $69.70   $69.70   $69.70  
  Purchase #3 $233.72   8.638%   $253.9087   $253.91   $253.90   $253.90  
  Purchase #4 $101.40   7.421%   $108.9249   $108.92   $108.90   $108.90  
  Purchase #5 $230.71   12.410%   $259.3411   $259.34   $259.35   $259.30  
  Purchase #6 $227.80   3.232%   $235.1625   $235.16   $235.15   $235.20  
  Purchase #7 $240.52   7.759%   $259.1819   $259.18   $259.20   $259.20  
  7 purchase totals = $1,320.37       $1,425.2360   $1,425.22   $1,425.20   $1,425.20