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 $57.97   13.442%   $65.7623   $65.76   $65.75   $65.80  
  Purchase #2 $208.86   10.222%   $230.2097   $230.21   $230.20   $230.20  
  Purchase #3 $232.49   10.811%   $257.6245   $257.62   $257.60   $257.60  
  Purchase #4 $46.27   5.443%   $48.7885   $48.79   $48.80   $48.80  
  Purchase #5 $122.98   6.848%   $131.4017   $131.40   $131.40   $131.40  
  Purchase #6 $183.25   9.776%   $201.1645   $201.16   $201.15   $201.20  
  Purchase #7 $177.25   4.530%   $185.2794   $185.28   $185.30   $185.30  
  7 purchase totals = $1,029.07       $1,120.2306   $1,120.22   $1,120.20   $1,120.30