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 $234.41   12.183%   $262.9682   $262.97   $262.95   $263.00  
  Purchase #2 $216.63   12.421%   $243.5376   $243.54   $243.55   $243.50  
  Purchase #3 $127.55   4.592%   $133.4071   $133.41   $133.40   $133.40  
  Purchase #4 $170.70   4.850%   $178.979   $178.98   $179.00   $179.00  
  Purchase #5 $56.65   8.832%   $61.6533   $61.65   $61.65   $61.70  
  Purchase #6 $136.32   9.231%   $148.9037   $148.90   $148.90   $148.90  
  Purchase #7 $240.93   7.762%   $259.631   $259.63   $259.65   $259.60  
  7 purchase totals = $1,183.19       $1,289.0799   $1,289.08   $1,289.10   $1,289.10