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 $87.41   12.871%   $98.6605   $98.66   $98.65   $98.70  
  Purchase #2 $93.37   5.117%   $98.1477   $98.15   $98.15   $98.10  
  Purchase #3 $182.69   7.388%   $196.1871   $196.19   $196.20   $196.20  
  Purchase #4 $149.41   3.298%   $154.3375   $154.34   $154.35   $154.30  
  Purchase #5 $188.26   4.668%   $197.048   $197.05   $197.05   $197.00  
  Purchase #6 $144.89   9.590%   $158.785   $158.79   $158.80   $158.80  
  Purchase #7 $226.61   10.572%   $250.5672   $250.57   $250.55   $250.60  
  7 purchase totals = $1,072.64       $1,153.7330   $1,153.75   $1,153.75   $1,153.70