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 $205.95   13.779%   $234.3279   $234.33   $234.35   $234.30  
  Purchase #2 $185.62   12.498%   $208.8188   $208.82   $208.80   $208.80  
  Purchase #3 $18.37   9.533%   $20.1212   $20.12   $20.10   $20.10  
  Purchase #4 $154.30   8.566%   $167.5173   $167.52   $167.50   $167.50  
  Purchase #5 $83.85   13.328%   $95.0255   $95.03   $95.05   $95.00  
  Purchase #6 $227.87   9.344%   $249.1622   $249.16   $249.15   $249.20  
  Purchase #7 $248.36   10.286%   $273.9063   $273.91   $273.90   $273.90  
  7 purchase totals = $1,124.32       $1,248.8792   $1,248.89   $1,248.85   $1,248.80