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 $54.72   12.640%   $61.6366   $61.64   $61.65   $61.60  
  Purchase #2 $93.28   5.565%   $98.471   $98.47   $98.45   $98.50  
  Purchase #3 $217.36   4.162%   $226.4065   $226.41   $226.40   $226.40  
  Purchase #4 $164.69   11.330%   $183.3494   $183.35   $183.35   $183.30  
  Purchase #5 $64.36   11.438%   $71.7215   $71.72   $71.70   $71.70  
  Purchase #6 $67.79   11.232%   $75.4042   $75.40   $75.40   $75.40  
  Purchase #7 $72.98   7.805%   $78.6761   $78.68   $78.70   $78.70  
  7 purchase totals = $735.18       $795.6653   $795.67   $795.65   $795.60