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 $191.41   12.792%   $215.8952   $215.90   $215.90   $215.90  
  Purchase #2 $239.64   11.495%   $267.1866   $267.19   $267.20   $267.20  
  Purchase #3 $126.92   7.417%   $136.3337   $136.33   $136.35   $136.30  
  Purchase #4 $233.65   5.569%   $246.662   $246.66   $246.65   $246.70  
  Purchase #5 $69.95   8.778%   $76.0902   $76.09   $76.10   $76.10  
  Purchase #6 $16.79   10.464%   $18.5469   $18.55   $18.55   $18.50  
  Purchase #7 $75.97   6.874%   $81.1922   $81.19   $81.20   $81.20  
  7 purchase totals = $954.33       $1,041.9068   $1,041.91   $1,041.95   $1,041.90