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 $18.61   4.858%   $19.5141   $19.51   $19.50   $19.50  
  Purchase #2 $31.62   9.587%   $34.6514   $34.65   $34.65   $34.70  
  Purchase #3 $218.55   3.366%   $225.9064   $225.91   $225.90   $225.90  
  Purchase #4 $106.67   4.322%   $111.2803   $111.28   $111.30   $111.30  
  Purchase #5 $239.36   9.301%   $261.6229   $261.62   $261.60   $261.60  
  Purchase #6 $241.93   7.394%   $259.8183   $259.82   $259.80   $259.80  
  Purchase #7 $63.54   8.539%   $68.9657   $68.97   $68.95   $69.00  
  7 purchase totals = $920.28       $981.7591   $981.76   $981.70   $981.80