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 $207.63   3.165%   $214.2015   $214.20   $214.20   $214.20  
  Purchase #2 $165.79   6.551%   $176.6509   $176.65   $176.65   $176.70  
  Purchase #3 $156.40   6.226%   $166.1375   $166.14   $166.15   $166.10  
  Purchase #4 $248.72   7.868%   $268.2893   $268.29   $268.30   $268.30  
  Purchase #5 $192.25   6.158%   $204.0888   $204.09   $204.10   $204.10  
  Purchase #6 $129.45   3.610%   $134.1231   $134.12   $134.10   $134.10  
  Purchase #7 $133.59   9.350%   $146.0807   $146.08   $146.10   $146.10  
  7 purchase totals = $1,233.83       $1,309.5718   $1,309.57   $1,309.60   $1,309.60