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 $189.29   11.832%   $211.6868   $211.69   $211.70   $211.70  
  Purchase #2 $246.99   12.836%   $278.6936   $278.69   $278.70   $278.70  
  Purchase #3 $59.66   7.730%   $64.2717   $64.27   $64.25   $64.30  
  Purchase #4 $169.42   7.675%   $182.423   $182.42   $182.40   $182.40  
  Purchase #5 $151.25   12.163%   $169.6465   $169.65   $169.65   $169.60  
  Purchase #6 $201.62   3.554%   $208.7856   $208.79   $208.80   $208.80  
  Purchase #7 $169.64   5.553%   $179.0601   $179.06   $179.05   $179.10  
  7 purchase totals = $1,187.87       $1,294.5673   $1,294.57   $1,294.55   $1,294.60