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 $101.76   5.553%   $107.4107   $107.41   $107.40   $107.40  
  Purchase #2 $95.49   3.359%   $98.6975   $98.70   $98.70   $98.70  
  Purchase #3 $205.65   7.242%   $220.5432   $220.54   $220.55   $220.50  
  Purchase #4 $166.65   5.863%   $176.4207   $176.42   $176.40   $176.40  
  Purchase #5 $127.50   6.774%   $136.1369   $136.14   $136.15   $136.10  
  Purchase #6 $125.56   10.312%   $138.5077   $138.51   $138.50   $138.50  
  Purchase #7 $171.94   7.475%   $184.7925   $184.79   $184.80   $184.80  
  7 purchase totals = $994.55       $1,062.5092   $1,062.51   $1,062.50   $1,062.40