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 $233.83   8.323%   $253.2917   $253.29   $253.30   $253.30  
  Purchase #2 $171.91   6.227%   $182.6148   $182.61   $182.60   $182.60  
  Purchase #3 $115.37   7.814%   $124.385   $124.39   $124.40   $124.40  
  Purchase #4 $240.92   6.511%   $256.6063   $256.61   $256.60   $256.60  
  Purchase #5 $171.80   7.327%   $184.3878   $184.39   $184.40   $184.40  
  Purchase #6 $23.25   5.420%   $24.5102   $24.51   $24.50   $24.50  
  Purchase #7 $160.80   4.806%   $168.528   $168.53   $168.55   $168.50  
  7 purchase totals = $1,117.88       $1,194.3238   $1,194.33   $1,194.35   $1,194.30