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 $193.49   13.330%   $219.2822   $219.28   $219.30   $219.30  
  Purchase #2 $57.36   11.689%   $64.0648   $64.06   $64.05   $64.10  
  Purchase #3 $76.43   12.554%   $86.025   $86.03   $86.05   $86.00  
  Purchase #4 $113.35   11.225%   $126.0735   $126.07   $126.05   $126.10  
  Purchase #5 $201.25   10.237%   $221.852   $221.85   $221.85   $221.90  
  Purchase #6 $242.93   6.324%   $258.2929   $258.29   $258.30   $258.30  
  Purchase #7 $163.27   12.342%   $183.4208   $183.42   $183.40   $183.40  
  7 purchase totals = $1,048.08       $1,159.0112   $1,159.00   $1,159.00   $1,159.10