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 $168.45   10.680%   $186.4405   $186.44   $186.45   $186.40  
  Purchase #2 $48.27   11.695%   $53.9152   $53.92   $53.90   $53.90  
  Purchase #3 $198.39   8.294%   $214.8445   $214.84   $214.85   $214.80  
  Purchase #4 $121.86   8.710%   $132.474   $132.47   $132.45   $132.50  
  Purchase #5 $133.33   6.768%   $142.3538   $142.35   $142.35   $142.40  
  Purchase #6 $235.34   11.745%   $262.9807   $262.98   $263.00   $263.00  
  Purchase #7 $248.55   5.341%   $261.8251   $261.83   $261.85   $261.80  
  7 purchase totals = $1,154.19       $1,254.8338   $1,254.83   $1,254.85   $1,254.80