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 $44.28   9.316%   $48.4051   $48.41   $48.40   $48.40  
  Purchase #2 $179.89   4.284%   $187.5965   $187.60   $187.60   $187.60  
  Purchase #3 $22.33   5.270%   $23.5068   $23.51   $23.50   $23.50  
  Purchase #4 $17.48   8.193%   $18.9121   $18.91   $18.90   $18.90  
  Purchase #5 $196.35   3.196%   $202.6253   $202.63   $202.65   $202.60  
  Purchase #6 $243.51   10.714%   $269.5997   $269.60   $269.60   $269.60  
  Purchase #7 $165.39   4.632%   $173.0509   $173.05   $173.05   $173.10  
  7 purchase totals = $869.23       $923.6964   $923.71   $923.70   $923.70