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 $22.84   7.154%   $24.474   $24.47   $24.45   $24.50  
  Purchase #2 $50.61   13.144%   $57.2622   $57.26   $57.25   $57.30  
  Purchase #3 $152.88   9.863%   $167.9586   $167.96   $167.95   $168.00  
  Purchase #4 $130.78   5.562%   $138.054   $138.05   $138.05   $138.10  
  Purchase #5 $71.61   4.212%   $74.6262   $74.63   $74.65   $74.60  
  Purchase #6 $208.53   8.390%   $226.0257   $226.03   $226.05   $226.00  
  Purchase #7 $208.80   8.625%   $226.809   $226.81   $226.80   $226.80  
  7 purchase totals = $846.05       $915.2097   $915.21   $915.20   $915.30