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 $194.76   8.244%   $210.816   $210.82   $210.80   $210.80  
  Purchase #2 $122.78   3.689%   $127.3094   $127.31   $127.30   $127.30  
  Purchase #3 $44.63   12.774%   $50.331   $50.33   $50.35   $50.30  
  Purchase #4 $17.93   5.568%   $18.9283   $18.93   $18.95   $18.90  
  Purchase #5 $196.93   6.108%   $208.9585   $208.96   $208.95   $209.00  
  Purchase #6 $139.40   11.540%   $155.4868   $155.49   $155.50   $155.50  
  Purchase #7 $118.50   6.509%   $126.2132   $126.21   $126.20   $126.20  
  7 purchase totals = $834.93       $898.0432   $898.05   $898.05   $898.00