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 $147.53   4.296%   $153.8679   $153.87   $153.85   $153.90  
  Purchase #2 $233.82   6.830%   $249.7899   $249.79   $249.80   $249.80  
  Purchase #3 $56.35   10.378%   $62.198   $62.20   $62.20   $62.20  
  Purchase #4 $247.95   9.624%   $271.8127   $271.81   $271.80   $271.80  
  Purchase #5 $181.82   6.812%   $194.2056   $194.21   $194.20   $194.20  
  Purchase #6 $191.97   8.271%   $207.8478   $207.85   $207.85   $207.80  
  Purchase #7 $27.72   5.660%   $29.289   $29.29   $29.30   $29.30  
  7 purchase totals = $1,087.16       $1,169.0109   $1,169.02   $1,169.00   $1,169.00