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 $54.66   13.173%   $61.8604   $61.86   $61.85   $61.90  
  Purchase #2 $114.34   13.864%   $130.1921   $130.19   $130.20   $130.20  
  Purchase #3 $24.79   11.321%   $27.5965   $27.60   $27.60   $27.60  
  Purchase #4 $32.39   8.224%   $35.0538   $35.05   $35.05   $35.10  
  Purchase #5 $192.72   3.233%   $198.9506   $198.95   $198.95   $199.00  
  Purchase #6 $237.36   6.468%   $252.7124   $252.71   $252.70   $252.70  
  Purchase #7 $187.30   4.397%   $195.5356   $195.54   $195.55   $195.50  
  7 purchase totals = $843.56       $901.9014   $901.90   $901.90   $902.00