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 $111.57   6.812%   $119.1701   $119.17   $119.15   $119.20  
  Purchase #2 $180.87   5.543%   $190.8956   $190.90   $190.90   $190.90  
  Purchase #3 $192.30   10.310%   $212.1261   $212.13   $212.15   $212.10  
  Purchase #4 $228.90   3.369%   $236.6116   $236.61   $236.60   $236.60  
  Purchase #5 $53.57   4.814%   $56.1489   $56.15   $56.15   $56.10  
  Purchase #6 $249.83   5.190%   $262.7962   $262.80   $262.80   $262.80  
  Purchase #7 $245.58   5.251%   $258.4754   $258.48   $258.50   $258.50  
  7 purchase totals = $1,262.62       $1,336.2239   $1,336.24   $1,336.25   $1,336.20