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 $22.83   7.491%   $24.5402   $24.54   $24.55   $24.50  
  Purchase #2 $126.97   9.764%   $139.3674   $139.37   $139.35   $139.40  
  Purchase #3 $43.61   7.848%   $47.0325   $47.03   $47.05   $47.00  
  Purchase #4 $236.43   9.348%   $258.5315   $258.53   $258.55   $258.50  
  Purchase #5 $106.49   4.434%   $111.2118   $111.21   $111.20   $111.20  
  Purchase #6 $64.90   4.291%   $67.6849   $67.68   $67.70   $67.70  
  Purchase #7 $212.95   13.175%   $241.0062   $241.01   $241.00   $241.00  
  7 purchase totals = $814.18       $889.3745   $889.37   $889.40   $889.30