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 $167.32   6.247%   $177.7725   $177.77   $177.75   $177.80  
  Purchase #2 $65.66   11.176%   $72.9982   $73.00   $73.00   $73.00  
  Purchase #3 $248.72   11.424%   $277.1338   $277.13   $277.15   $277.10  
  Purchase #4 $175.63   5.466%   $185.2299   $185.23   $185.25   $185.20  
  Purchase #5 $108.36   8.325%   $117.381   $117.38   $117.40   $117.40  
  Purchase #6 $77.45   4.110%   $80.6332   $80.63   $80.65   $80.60  
  Purchase #7 $33.39   8.203%   $36.129   $36.13   $36.15   $36.10  
  7 purchase totals = $876.53       $947.2776   $947.27   $947.35   $947.20