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 $59.73   9.143%   $65.1911   $65.19   $65.20   $65.20  
  Purchase #2 $224.67   10.622%   $248.5344   $248.53   $248.55   $248.50  
  Purchase #3 $18.60   6.161%   $19.7459   $19.75   $19.75   $19.70  
  Purchase #4 $120.29   3.678%   $124.7143   $124.71   $124.70   $124.70  
  Purchase #5 $221.80   8.610%   $240.897   $240.90   $240.90   $240.90  
  Purchase #6 $250.33   5.374%   $263.7827   $263.78   $263.80   $263.80  
  Purchase #7 $119.68   7.174%   $128.2658   $128.27   $128.25   $128.30  
  7 purchase totals = $1,015.10       $1,091.1312   $1,091.13   $1,091.15   $1,091.10