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 $237.36   11.612%   $264.9222   $264.92   $264.90   $264.90  
  Purchase #2 $175.75   9.468%   $192.39   $192.39   $192.40   $192.40  
  Purchase #3 $46.48   13.161%   $52.5972   $52.60   $52.60   $52.60  
  Purchase #4 $182.75   10.365%   $201.692   $201.69   $201.70   $201.70  
  Purchase #5 $173.32   11.173%   $192.685   $192.69   $192.70   $192.70  
  Purchase #6 $204.86   3.186%   $211.3868   $211.39   $211.40   $211.40  
  Purchase #7 $129.57   12.724%   $146.0565   $146.06   $146.05   $146.10  
  7 purchase totals = $1,150.09       $1,261.7297   $1,261.74   $1,261.75   $1,261.80