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 $57.92   4.305%   $60.4135   $60.41   $60.40   $60.40  
  Purchase #2 $118.96   12.782%   $134.1655   $134.17   $134.15   $134.20  
  Purchase #3 $177.97   13.382%   $201.7859   $201.79   $201.80   $201.80  
  Purchase #4 $14.91   13.483%   $16.9203   $16.92   $16.90   $16.90  
  Purchase #5 $216.97   4.301%   $226.3019   $226.30   $226.30   $226.30  
  Purchase #6 $8.93   8.276%   $9.669   $9.67   $9.65   $9.70  
  Purchase #7 $250.93   13.255%   $284.1908   $284.19   $284.20   $284.20  
  7 purchase totals = $846.59       $933.4469   $933.45   $933.40   $933.50