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 $24.93   8.104%   $26.9503   $26.95   $26.95   $27.00  
  Purchase #2 $138.83   3.557%   $143.7682   $143.77   $143.75   $143.80  
  Purchase #3 $211.68   7.556%   $227.6745   $227.67   $227.65   $227.70  
  Purchase #4 $56.59   9.201%   $61.7968   $61.80   $61.80   $61.80  
  Purchase #5 $144.42   12.455%   $162.4075   $162.41   $162.40   $162.40  
  Purchase #6 $168.95   4.345%   $176.2909   $176.29   $176.30   $176.30  
  Purchase #7 $80.29   7.635%   $86.4201   $86.42   $86.40   $86.40  
  7 purchase totals = $825.69       $885.3083   $885.31   $885.25   $885.40