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 $208.74   8.652%   $226.8002   $226.80   $226.80   $226.80  
  Purchase #2 $35.25   10.610%   $38.99   $38.99   $39.00   $39.00  
  Purchase #3 $44.69   12.374%   $50.2199   $50.22   $50.20   $50.20  
  Purchase #4 $218.99   6.141%   $232.4382   $232.44   $232.45   $232.40  
  Purchase #5 $183.75   6.809%   $196.2615   $196.26   $196.25   $196.30  
  Purchase #6 $155.85   3.698%   $161.6133   $161.61   $161.60   $161.60  
  Purchase #7 $97.55   9.622%   $106.9363   $106.94   $106.95   $106.90  
  7 purchase totals = $944.82       $1,013.2594   $1,013.26   $1,013.25   $1,013.20