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 $34.28   12.386%   $38.5259   $38.53   $38.55   $38.50  
  Purchase #2 $9.26   3.704%   $9.603   $9.60   $9.60   $9.60  
  Purchase #3 $200.52   3.561%   $207.6605   $207.66   $207.65   $207.70  
  Purchase #4 $217.92   6.316%   $231.6838   $231.68   $231.70   $231.70  
  Purchase #5 $61.35   11.489%   $68.3985   $68.40   $68.40   $68.40  
  Purchase #6 $181.62   4.872%   $190.4685   $190.47   $190.45   $190.50  
  Purchase #7 $144.28   5.545%   $152.2803   $152.28   $152.30   $152.30  
  7 purchase totals = $849.23       $898.6205   $898.62   $898.65   $898.70