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 $124.74   9.496%   $136.5853   $136.59   $136.60   $136.60  
  Purchase #2 $162.26   8.372%   $175.8444   $175.84   $175.85   $175.80  
  Purchase #3 $90.40   4.671%   $94.6226   $94.62   $94.60   $94.60  
  Purchase #4 $167.33   5.750%   $176.9515   $176.95   $176.95   $177.00  
  Purchase #5 $176.63   11.469%   $196.8877   $196.89   $196.90   $196.90  
  Purchase #6 $173.40   10.744%   $192.0301   $192.03   $192.05   $192.00  
  Purchase #7 $111.55   11.219%   $124.0648   $124.06   $124.05   $124.10  
  7 purchase totals = $1,006.31       $1,096.9864   $1,096.98   $1,097.00   $1,097.00