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 $176.77   3.557%   $183.0577   $183.06   $183.05   $183.10  
  Purchase #2 $44.81   8.762%   $48.7363   $48.74   $48.75   $48.70  
  Purchase #3 $199.86   7.552%   $214.9534   $214.95   $214.95   $215.00  
  Purchase #4 $53.49   5.610%   $56.4908   $56.49   $56.50   $56.50  
  Purchase #5 $69.49   12.397%   $78.1047   $78.10   $78.10   $78.10  
  Purchase #6 $161.45   5.321%   $170.0408   $170.04   $170.05   $170.00  
  Purchase #7 $246.80   10.278%   $272.1661   $272.17   $272.15   $272.20  
  7 purchase totals = $952.67       $1,023.5498   $1,023.55   $1,023.55   $1,023.60