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 $98.83   8.122%   $106.857   $106.86   $106.85   $106.90  
  Purchase #2 $24.52   5.661%   $25.9081   $25.91   $25.90   $25.90  
  Purchase #3 $59.75   3.672%   $61.944   $61.94   $61.95   $61.90  
  Purchase #4 $241.61   10.278%   $266.4427   $266.44   $266.45   $266.40  
  Purchase #5 $162.76   9.566%   $178.3296   $178.33   $178.35   $178.30  
  Purchase #6 $35.66   8.483%   $38.685   $38.69   $38.70   $38.70  
  Purchase #7 $226.75   3.537%   $234.7701   $234.77   $234.75   $234.80  
  7 purchase totals = $849.88       $912.9365   $912.94   $912.95   $912.90