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 $210.81   11.385%   $234.8107   $234.81   $234.80   $234.80  
  Purchase #2 $156.47   4.617%   $163.6942   $163.69   $163.70   $163.70  
  Purchase #3 $20.25   4.790%   $21.22   $21.22   $21.20   $21.20  
  Purchase #4 $124.49   13.458%   $141.2439   $141.24   $141.25   $141.20  
  Purchase #5 $226.95   11.234%   $252.4456   $252.45   $252.45   $252.40  
  Purchase #6 $91.36   10.382%   $100.845   $100.85   $100.85   $100.80  
  Purchase #7 $180.95   13.248%   $204.9223   $204.92   $204.90   $204.90  
  7 purchase totals = $1,011.28       $1,119.1817   $1,119.18   $1,119.15   $1,119.00