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 $91.62   4.779%   $95.9985   $96.00   $96.00   $96.00  
  Purchase #2 $246.61   12.386%   $277.1551   $277.16   $277.15   $277.20  
  Purchase #3 $143.97   7.149%   $154.2624   $154.26   $154.25   $154.30  
  Purchase #4 $179.26   13.138%   $202.8112   $202.81   $202.80   $202.80  
  Purchase #5 $232.69   9.694%   $255.247   $255.25   $255.25   $255.20  
  Purchase #6 $208.46   9.866%   $229.0267   $229.03   $229.05   $229.00  
  Purchase #7 $148.42   10.213%   $163.5781   $163.58   $163.60   $163.60  
  7 purchase totals = $1,251.03       $1,378.0790   $1,378.09   $1,378.10   $1,378.10