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 $140.40   11.152%   $156.0574   $156.06   $156.05   $156.10  
  Purchase #2 $157.28   13.478%   $178.4782   $178.48   $178.50   $178.50  
  Purchase #3 $22.99   11.142%   $25.5515   $25.55   $25.55   $25.60  
  Purchase #4 $110.54   4.443%   $115.4513   $115.45   $115.45   $115.50  
  Purchase #5 $76.61   5.614%   $80.9109   $80.91   $80.90   $80.90  
  Purchase #6 $193.74   10.382%   $213.8541   $213.85   $213.85   $213.90  
  Purchase #7 $151.61   4.741%   $158.7978   $158.80   $158.80   $158.80  
  7 purchase totals = $853.17       $929.1012   $929.10   $929.10   $929.30