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 $205.36   9.255%   $224.3661   $224.37   $224.35   $224.40  
  Purchase #2 $78.79   4.652%   $82.4553   $82.46   $82.45   $82.50  
  Purchase #3 $62.37   9.834%   $68.5035   $68.50   $68.50   $68.50  
  Purchase #4 $31.86   10.806%   $35.3028   $35.30   $35.30   $35.30  
  Purchase #5 $48.75   6.402%   $51.871   $51.87   $51.85   $51.90  
  Purchase #6 $29.73   3.590%   $30.7973   $30.80   $30.80   $30.80  
  Purchase #7 $219.81   12.861%   $248.0798   $248.08   $248.10   $248.10  
  7 purchase totals = $676.67       $741.3758   $741.38   $741.35   $741.50