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 $171.93   11.852%   $192.3071   $192.31   $192.30   $192.30  
  Purchase #2 $24.45   4.727%   $25.6058   $25.61   $25.60   $25.60  
  Purchase #3 $158.81   11.197%   $176.592   $176.59   $176.60   $176.60  
  Purchase #4 $35.30   10.653%   $39.0605   $39.06   $39.05   $39.10  
  Purchase #5 $210.38   6.752%   $224.5849   $224.58   $224.60   $224.60  
  Purchase #6 $245.95   5.620%   $259.7724   $259.77   $259.75   $259.80  
  Purchase #7 $182.95   4.114%   $190.4766   $190.48   $190.50   $190.50  
  7 purchase totals = $1,029.77       $1,108.3993   $1,108.40   $1,108.40   $1,108.50