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 $103.25   11.331%   $114.9493   $114.95   $114.95   $114.90  
  Purchase #2 $178.73   11.309%   $198.9426   $198.94   $198.95   $198.90  
  Purchase #3 $127.26   6.271%   $135.2405   $135.24   $135.25   $135.20  
  Purchase #4 $162.85   8.331%   $176.417   $176.42   $176.40   $176.40  
  Purchase #5 $227.25   13.670%   $258.3151   $258.32   $258.30   $258.30  
  Purchase #6 $206.61   6.637%   $220.3227   $220.32   $220.30   $220.30  
  Purchase #7 $204.37   10.834%   $226.5114   $226.51   $226.50   $226.50  
  7 purchase totals = $1,210.32       $1,330.6986   $1,330.70   $1,330.65   $1,330.50