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 $62.97   11.492%   $70.2065   $70.21   $70.20   $70.20  
  Purchase #2 $119.42   6.562%   $127.2563   $127.26   $127.25   $127.30  
  Purchase #3 $48.99   8.128%   $52.9719   $52.97   $52.95   $53.00  
  Purchase #4 $150.54   11.129%   $167.2936   $167.29   $167.30   $167.30  
  Purchase #5 $113.25   11.657%   $126.4516   $126.45   $126.45   $126.50  
  Purchase #6 $180.99   10.631%   $200.231   $200.23   $200.25   $200.20  
  Purchase #7 $69.54   11.688%   $77.6678   $77.67   $77.65   $77.70  
  7 purchase totals = $745.70       $822.0787   $822.08   $822.05   $822.20