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 $47.61   11.808%   $53.2318   $53.23   $53.25   $53.20  
  Purchase #2 $241.49   11.764%   $269.8989   $269.90   $269.90   $269.90  
  Purchase #3 $187.92   4.719%   $196.7879   $196.79   $196.80   $196.80  
  Purchase #4 $77.77   7.343%   $83.4807   $83.48   $83.50   $83.50  
  Purchase #5 $47.50   9.409%   $51.9693   $51.97   $51.95   $52.00  
  Purchase #6 $199.97   8.139%   $216.2456   $216.25   $216.25   $216.20  
  Purchase #7 $175.97   5.788%   $186.1551   $186.16   $186.15   $186.20  
  7 purchase totals = $978.23       $1,057.7693   $1,057.78   $1,057.80   $1,057.80