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 $238.71   4.552%   $249.5761   $249.58   $249.60   $249.60  
  Purchase #2 $102.32   4.151%   $106.5673   $106.57   $106.55   $106.60  
  Purchase #3 $49.77   7.489%   $53.4973   $53.50   $53.50   $53.50  
  Purchase #4 $227.38   8.723%   $247.2144   $247.21   $247.20   $247.20  
  Purchase #5 $178.60   10.645%   $197.612   $197.61   $197.60   $197.60  
  Purchase #6 $51.40   8.181%   $55.605   $55.61   $55.60   $55.60  
  Purchase #7 $13.59   9.806%   $14.9226   $14.92   $14.90   $14.90  
  7 purchase totals = $861.77       $924.9947   $925.00   $924.95   $925.00