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 $206.95   9.564%   $226.7427   $226.74   $226.75   $226.70  
  Purchase #2 $75.35   11.161%   $83.7598   $83.76   $83.75   $83.80  
  Purchase #3 $236.76   5.833%   $250.5702   $250.57   $250.55   $250.60  
  Purchase #4 $167.41   5.308%   $176.2961   $176.30   $176.30   $176.30  
  Purchase #5 $147.31   9.269%   $160.9642   $160.96   $160.95   $161.00  
  Purchase #6 $59.83   4.278%   $62.3895   $62.39   $62.40   $62.40  
  Purchase #7 $58.75   7.659%   $63.2497   $63.25   $63.25   $63.20  
  7 purchase totals = $952.36       $1,023.9722   $1,023.97   $1,023.95   $1,024.00