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 $50.67   11.623%   $56.5594   $56.56   $56.55   $56.60  
  Purchase #2 $15.89   4.412%   $16.5911   $16.59   $16.60   $16.60  
  Purchase #3 $137.83   10.451%   $152.2346   $152.23   $152.25   $152.20  
  Purchase #4 $213.89   3.619%   $221.6307   $221.63   $221.65   $221.60  
  Purchase #5 $163.42   3.504%   $169.1462   $169.15   $169.15   $169.10  
  Purchase #6 $209.75   9.650%   $229.9909   $229.99   $230.00   $230.00  
  Purchase #7 $196.31   8.854%   $213.6913   $213.69   $213.70   $213.70  
  7 purchase totals = $987.76       $1,059.8442   $1,059.84   $1,059.90   $1,059.80