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 $38.64   13.705%   $43.9356   $43.94   $43.95   $43.90  
  Purchase #2 $116.67   8.491%   $126.5764   $126.58   $126.60   $126.60  
  Purchase #3 $220.33   6.235%   $234.0676   $234.07   $234.05   $234.10  
  Purchase #4 $152.60   9.786%   $167.5334   $167.53   $167.55   $167.50  
  Purchase #5 $99.49   6.401%   $105.8584   $105.86   $105.85   $105.90  
  Purchase #6 $192.55   3.768%   $199.8053   $199.81   $199.80   $199.80  
  Purchase #7 $74.55   13.350%   $84.5024   $84.50   $84.50   $84.50  
  7 purchase totals = $894.83       $962.2791   $962.29   $962.30   $962.30