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 $169.54   13.235%   $191.9786   $191.98   $192.00   $192.00  
  Purchase #2 $98.61   3.598%   $102.158   $102.16   $102.15   $102.20  
  Purchase #3 $30.99   8.711%   $33.6895   $33.69   $33.70   $33.70  
  Purchase #4 $59.31   3.839%   $61.5869   $61.59   $61.60   $61.60  
  Purchase #5 $229.40   8.372%   $248.6054   $248.61   $248.60   $248.60  
  Purchase #6 $33.63   7.721%   $36.2266   $36.23   $36.25   $36.20  
  Purchase #7 $215.66   9.701%   $236.5812   $236.58   $236.60   $236.60  
  7 purchase totals = $837.14       $910.8262   $910.84   $910.90   $910.90