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 $246.60   8.783%   $268.2589   $268.26   $268.25   $268.30  
  Purchase #2 $16.91   11.136%   $18.7931   $18.79   $18.80   $18.80  
  Purchase #3 $148.57   4.744%   $155.6182   $155.62   $155.60   $155.60  
  Purchase #4 $113.52   6.864%   $121.312   $121.31   $121.30   $121.30  
  Purchase #5 $61.71   3.617%   $63.9421   $63.94   $63.95   $63.90  
  Purchase #6 $168.83   6.118%   $179.159   $179.16   $179.15   $179.20  
  Purchase #7 $162.98   3.120%   $168.065   $168.07   $168.05   $168.10  
  7 purchase totals = $919.12       $975.1483   $975.15   $975.10   $975.20