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 $231.71   9.198%   $253.0227   $253.02   $253.00   $253.00  
  Purchase #2 $148.76   8.371%   $161.2127   $161.21   $161.20   $161.20  
  Purchase #3 $68.55   8.857%   $74.6215   $74.62   $74.60   $74.60  
  Purchase #4 $196.62   11.455%   $219.1428   $219.14   $219.15   $219.10  
  Purchase #5 $175.74   5.218%   $184.9101   $184.91   $184.90   $184.90  
  Purchase #6 $226.29   10.348%   $249.7065   $249.71   $249.70   $249.70  
  Purchase #7 $229.45   13.429%   $260.2628   $260.26   $260.25   $260.30  
  7 purchase totals = $1,277.12       $1,402.8791   $1,402.87   $1,402.80   $1,402.80