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 $105.44   13.576%   $119.7545   $119.75   $119.75   $119.80  
  Purchase #2 $6.25   4.408%   $6.5255   $6.53   $6.55   $6.50  
  Purchase #3 $205.28   13.446%   $232.8819   $232.88   $232.90   $232.90  
  Purchase #4 $46.66   13.488%   $52.9535   $52.95   $52.95   $53.00  
  Purchase #5 $128.57   4.244%   $134.0265   $134.03   $134.05   $134.00  
  Purchase #6 $195.49   8.760%   $212.6149   $212.61   $212.60   $212.60  
  Purchase #7 $235.61   5.691%   $249.0186   $249.02   $249.00   $249.00  
  7 purchase totals = $923.30       $1,007.7754   $1,007.77   $1,007.80   $1,007.80