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 $130.86   4.146%   $136.2855   $136.29   $136.30   $136.30  
  Purchase #2 $233.55   6.558%   $248.8662   $248.87   $248.85   $248.90  
  Purchase #3 $124.65   3.346%   $128.8208   $128.82   $128.80   $128.80  
  Purchase #4 $96.29   13.667%   $109.45   $109.45   $109.45   $109.50  
  Purchase #5 $54.74   6.453%   $58.2724   $58.27   $58.25   $58.30  
  Purchase #6 $215.90   4.860%   $226.3927   $226.39   $226.40   $226.40  
  Purchase #7 $208.85   13.353%   $236.7377   $236.74   $236.75   $236.70  
  7 purchase totals = $1,064.84       $1,144.8253   $1,144.83   $1,144.80   $1,144.90