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 $158.29   6.552%   $168.6612   $168.66   $168.65   $168.70  
  Purchase #2 $67.98   10.311%   $74.9894   $74.99   $75.00   $75.00  
  Purchase #3 $61.86   13.186%   $70.0169   $70.02   $70.00   $70.00  
  Purchase #4 $164.96   13.306%   $186.9096   $186.91   $186.90   $186.90  
  Purchase #5 $141.93   9.105%   $154.8527   $154.85   $154.85   $154.90  
  Purchase #6 $183.50   9.269%   $200.5086   $200.51   $200.50   $200.50  
  Purchase #7 $153.44   13.564%   $174.2526   $174.25   $174.25   $174.30  
  7 purchase totals = $931.96       $1,030.1910   $1,030.19   $1,030.15   $1,030.30