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 $22.69   7.106%   $24.3024   $24.30   $24.30   $24.30  
  Purchase #2 $221.46   9.472%   $242.4367   $242.44   $242.45   $242.40  
  Purchase #3 $50.90   4.681%   $53.2826   $53.28   $53.30   $53.30  
  Purchase #4 $160.50   10.803%   $177.8388   $177.84   $177.85   $177.80  
  Purchase #5 $162.46   5.705%   $171.7283   $171.73   $171.75   $171.70  
  Purchase #6 $174.95   10.541%   $193.3915   $193.39   $193.40   $193.40  
  Purchase #7 $237.31   9.556%   $259.9873   $259.99   $260.00   $260.00  
  7 purchase totals = $1,030.27       $1,122.9676   $1,122.97   $1,123.05   $1,122.90