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 $14.40   11.484%   $16.0537   $16.05   $16.05   $16.10  
  Purchase #2 $156.27   6.538%   $166.4869   $166.49   $166.50   $166.50  
  Purchase #3 $105.36   13.413%   $119.4919   $119.49   $119.50   $119.50  
  Purchase #4 $153.83   11.537%   $171.5774   $171.58   $171.60   $171.60  
  Purchase #5 $51.95   8.280%   $56.2515   $56.25   $56.25   $56.30  
  Purchase #6 $69.25   10.495%   $76.5178   $76.52   $76.50   $76.50  
  Purchase #7 $125.33   4.744%   $131.2757   $131.28   $131.30   $131.30  
  7 purchase totals = $676.39       $737.6549   $737.66   $737.70   $737.80