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 $152.57   6.605%   $162.6472   $162.65   $162.65   $162.60  
  Purchase #2 $32.83   8.305%   $35.5565   $35.56   $35.55   $35.60  
  Purchase #3 $225.39   13.734%   $256.3451   $256.35   $256.35   $256.30  
  Purchase #4 $94.87   9.197%   $103.5952   $103.60   $103.60   $103.60  
  Purchase #5 $176.25   8.157%   $190.6267   $190.63   $190.65   $190.60  
  Purchase #6 $243.94   3.703%   $252.9731   $252.97   $252.95   $253.00  
  Purchase #7 $214.86   11.516%   $239.6033   $239.60   $239.60   $239.60  
  7 purchase totals = $1,140.71       $1,241.3471   $1,241.36   $1,241.35   $1,241.30