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 $71.54   3.231%   $73.8515   $73.85   $73.85   $73.90  
  Purchase #2 $128.27   12.773%   $144.6539   $144.65   $144.65   $144.70  
  Purchase #3 $200.99   6.762%   $214.5809   $214.58   $214.60   $214.60  
  Purchase #4 $236.65   10.769%   $262.1348   $262.13   $262.15   $262.10  
  Purchase #5 $77.72   11.642%   $86.7682   $86.77   $86.75   $86.80  
  Purchase #6 $157.78   10.577%   $174.4684   $174.47   $174.45   $174.50  
  Purchase #7 $225.96   11.621%   $252.2188   $252.22   $252.20   $252.20  
  7 purchase totals = $1,098.91       $1,208.6765   $1,208.67   $1,208.65   $1,208.80