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 $139.67   10.418%   $154.2208   $154.22   $154.20   $154.20  
  Purchase #2 $153.62   8.639%   $166.8912   $166.89   $166.90   $166.90  
  Purchase #3 $18.40   11.602%   $20.5348   $20.53   $20.55   $20.50  
  Purchase #4 $37.51   9.823%   $41.1946   $41.19   $41.20   $41.20  
  Purchase #5 $174.61   11.448%   $194.5994   $194.60   $194.60   $194.60  
  Purchase #6 $181.29   3.547%   $187.7204   $187.72   $187.70   $187.70  
  Purchase #7 $228.48   9.268%   $249.6555   $249.66   $249.65   $249.70  
  7 purchase totals = $933.58       $1,014.8167   $1,014.81   $1,014.80   $1,014.80