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 $61.66   5.231%   $64.8854   $64.89   $64.90   $64.90  
  Purchase #2 $208.98   6.278%   $222.0998   $222.10   $222.10   $222.10  
  Purchase #3 $114.57   5.584%   $120.9676   $120.97   $120.95   $121.00  
  Purchase #4 $28.95   9.718%   $31.7634   $31.76   $31.75   $31.80  
  Purchase #5 $198.41   11.636%   $221.497   $221.50   $221.50   $221.50  
  Purchase #6 $33.73   12.597%   $37.979   $37.98   $38.00   $38.00  
  Purchase #7 $230.60   3.659%   $239.0377   $239.04   $239.05   $239.00  
  7 purchase totals = $876.90       $938.2299   $938.24   $938.25   $938.30