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 $239.43   11.617%   $267.2446   $267.24   $267.25   $267.20  
  Purchase #2 $41.36   8.656%   $44.9401   $44.94   $44.95   $44.90  
  Purchase #3 $147.33   11.804%   $164.7208   $164.72   $164.70   $164.70  
  Purchase #4 $101.67   6.530%   $108.3091   $108.31   $108.30   $108.30  
  Purchase #5 $30.83   9.653%   $33.806   $33.81   $33.80   $33.80  
  Purchase #6 $161.78   4.318%   $168.7657   $168.77   $168.75   $168.80  
  Purchase #7 $5.54   8.535%   $6.0128   $6.01   $6.00   $6.00  
  7 purchase totals = $727.94       $793.7991   $793.80   $793.75   $793.70