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 $61.60   9.731%   $67.5943   $67.59   $67.60   $67.60  
  Purchase #2 $226.78   4.528%   $237.0486   $237.05   $237.05   $237.00  
  Purchase #3 $26.95   13.267%   $30.5255   $30.53   $30.55   $30.50  
  Purchase #4 $101.84   4.119%   $106.0348   $106.03   $106.05   $106.00  
  Purchase #5 $94.65   8.228%   $102.4378   $102.44   $102.45   $102.40  
  Purchase #6 $46.68   9.640%   $51.18   $51.18   $51.20   $51.20  
  Purchase #7 $213.40   6.777%   $227.8621   $227.86   $227.85   $227.90  
  7 purchase totals = $771.90       $822.6831   $822.68   $822.75   $822.60