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 $176.76   13.779%   $201.1158   $201.12   $201.10   $201.10  
  Purchase #2 $137.46   13.801%   $156.4309   $156.43   $156.45   $156.40  
  Purchase #3 $175.46   10.501%   $193.8851   $193.89   $193.90   $193.90  
  Purchase #4 $192.68   7.542%   $207.2119   $207.21   $207.20   $207.20  
  Purchase #5 $32.32   4.683%   $33.8335   $33.83   $33.85   $33.80  
  Purchase #6 $24.99   4.655%   $26.1533   $26.15   $26.15   $26.20  
  Purchase #7 $171.76   10.457%   $189.7209   $189.72   $189.70   $189.70  
  7 purchase totals = $911.43       $1,008.3514   $1,008.35   $1,008.35   $1,008.30