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 $201.41   12.834%   $227.259   $227.26   $227.25   $227.30  
  Purchase #2 $20.69   13.465%   $23.4759   $23.48   $23.50   $23.50  
  Purchase #3 $240.95   3.848%   $250.2218   $250.22   $250.20   $250.20  
  Purchase #4 $181.53   5.157%   $190.8915   $190.89   $190.90   $190.90  
  Purchase #5 $70.27   4.384%   $73.3506   $73.35   $73.35   $73.40  
  Purchase #6 $142.77   6.597%   $152.1885   $152.19   $152.20   $152.20  
  Purchase #7 $157.27   11.834%   $175.8813   $175.88   $175.90   $175.90  
  7 purchase totals = $1,014.89       $1,093.2686   $1,093.27   $1,093.30   $1,093.40