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 $181.95   8.230%   $196.9245   $196.92   $196.90   $196.90  
  Purchase #2 $214.75   6.156%   $227.97   $227.97   $227.95   $228.00  
  Purchase #3 $44.41   12.544%   $49.9808   $49.98   $50.00   $50.00  
  Purchase #4 $181.43   3.227%   $187.2847   $187.28   $187.30   $187.30  
  Purchase #5 $232.80   13.475%   $264.1698   $264.17   $264.15   $264.20  
  Purchase #6 $32.46   5.589%   $34.2742   $34.27   $34.25   $34.30  
  Purchase #7 $87.28   12.872%   $98.5147   $98.51   $98.50   $98.50  
  7 purchase totals = $975.08       $1,059.1187   $1,059.10   $1,059.05   $1,059.20