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 $240.94   11.458%   $268.5469   $268.55   $268.55   $268.50  
  Purchase #2 $11.51   9.739%   $12.631   $12.63   $12.65   $12.60  
  Purchase #3 $39.96   10.163%   $44.0211   $44.02   $44.00   $44.00  
  Purchase #4 $70.52   12.862%   $79.5903   $79.59   $79.60   $79.60  
  Purchase #5 $55.47   4.705%   $58.0799   $58.08   $58.10   $58.10  
  Purchase #6 $151.82   8.417%   $164.5987   $164.60   $164.60   $164.60  
  Purchase #7 $229.83   12.355%   $258.2255   $258.23   $258.25   $258.20  
  7 purchase totals = $800.05       $885.6934   $885.70   $885.75   $885.60