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 $192.47   12.189%   $215.9302   $215.93   $215.95   $215.90  
  Purchase #2 $52.85   9.158%   $57.69   $57.69   $57.70   $57.70  
  Purchase #3 $54.68   7.585%   $58.8275   $58.83   $58.85   $58.80  
  Purchase #4 $125.32   9.694%   $137.4685   $137.47   $137.45   $137.50  
  Purchase #5 $141.74   13.744%   $161.2207   $161.22   $161.20   $161.20  
  Purchase #6 $186.92   3.788%   $194.0005   $194.00   $194.00   $194.00  
  Purchase #7 $151.82   5.558%   $160.2582   $160.26   $160.25   $160.30  
  7 purchase totals = $905.80       $985.3956   $985.40   $985.40   $985.40