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 $206.48   9.327%   $225.7384   $225.74   $225.75   $225.70  
  Purchase #2 $56.49   10.316%   $62.3175   $62.32   $62.30   $62.30  
  Purchase #3 $34.82   10.398%   $38.4406   $38.44   $38.45   $38.40  
  Purchase #4 $161.40   6.231%   $171.4568   $171.46   $171.45   $171.50  
  Purchase #5 $201.79   4.561%   $210.9936   $210.99   $211.00   $211.00  
  Purchase #6 $237.42   5.598%   $250.7108   $250.71   $250.70   $250.70  
  Purchase #7 $92.69   4.441%   $96.8064   $96.81   $96.80   $96.80  
  7 purchase totals = $991.09       $1,056.4641   $1,056.47   $1,056.45   $1,056.40