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 $64.59   13.421%   $73.2586   $73.26   $73.25   $73.30  
  Purchase #2 $126.99   7.627%   $136.6755   $136.68   $136.70   $136.70  
  Purchase #3 $208.50   13.286%   $236.2013   $236.20   $236.20   $236.20  
  Purchase #4 $34.31   6.567%   $36.5631   $36.56   $36.55   $36.60  
  Purchase #5 $5.82   12.445%   $6.5443   $6.54   $6.55   $6.50  
  Purchase #6 $160.50   5.202%   $168.8492   $168.85   $168.85   $168.80  
  Purchase #7 $156.78   11.213%   $174.3597   $174.36   $174.35   $174.40  
  7 purchase totals = $757.49       $832.4517   $832.45   $832.45   $832.50